diff --git a/src/DiskAdaptor.cc b/src/DiskAdaptor.cc
index 641c94de..a307c377 100644
--- a/src/DiskAdaptor.cc
+++ b/src/DiskAdaptor.cc
@@ -34,12 +34,12 @@
 /* copyright --> */
 #include "DiskAdaptor.h"
 #include "FileEntry.h"
+#include "OpenedFileCounter.h"
 
 namespace aria2 {
 
 DiskAdaptor::DiskAdaptor()
-  : fileAllocationMethod_(FILE_ALLOC_ADAPTIVE),
-    requestGroupMan_(nullptr)
+  : fileAllocationMethod_(FILE_ALLOC_ADAPTIVE)
 {}
 
 DiskAdaptor::~DiskAdaptor() {}
diff --git a/src/DiskAdaptor.h b/src/DiskAdaptor.h
index 114f904c..bb070707 100644
--- a/src/DiskAdaptor.h
+++ b/src/DiskAdaptor.h
@@ -48,7 +48,7 @@ namespace aria2 {
 class FileEntry;
 class FileAllocationIterator;
 class WrDiskCacheEntry;
-class RequestGroupMan;
+class OpenedFileCounter;
 
 class DiskAdaptor:public BinaryStream {
 public:
@@ -125,21 +125,23 @@ public:
   // Returns the number of closed files.
   virtual size_t tryCloseFile(size_t numClose) { return 0; }
 
-  void setRequestGroupMan(RequestGroupMan* rgman)
+  void setOpenedFileCounter
+  (std::shared_ptr<OpenedFileCounter> openedFileCounter)
   {
-    requestGroupMan_ = rgman;
+    openedFileCounter_ = std::move(openedFileCounter);
   }
 
-  RequestGroupMan* getRequestGroupMan() const
+  const std::shared_ptr<OpenedFileCounter>& getOpenedFileCounter() const
   {
-    return requestGroupMan_;
+    return openedFileCounter_;
   }
+
 private:
   std::vector<std::shared_ptr<FileEntry> > fileEntries_;
 
   FileAllocationMethod fileAllocationMethod_;
 
-  RequestGroupMan* requestGroupMan_;
+  std::shared_ptr<OpenedFileCounter> openedFileCounter_;
 };
 
 } // namespace aria2
diff --git a/src/Makefile.am b/src/Makefile.am
index 89f4b8ae..fb201e33 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -264,7 +264,8 @@ SRCS =  \
 	WatchProcessCommand.cc WatchProcessCommand.h\
 	WrDiskCache.cc WrDiskCache.h\
 	WrDiskCacheEntry.cc WrDiskCacheEntry.h\
-	XmlRpcRequestParserController.cc XmlRpcRequestParserController.h
+	XmlRpcRequestParserController.cc XmlRpcRequestParserController.h\
+	OpenedFileCounter.cc OpenedFileCounter.h
 
 if ANDROID
 SRCS += android/android.c
diff --git a/src/MultiDiskAdaptor.cc b/src/MultiDiskAdaptor.cc
index 825b04cc..4a2b0ec4 100644
--- a/src/MultiDiskAdaptor.cc
+++ b/src/MultiDiskAdaptor.cc
@@ -51,7 +51,7 @@
 #include "LogFactory.h"
 #include "SimpleRandomizer.h"
 #include "WrDiskCacheEntry.h"
-#include "RequestGroupMan.h"
+#include "OpenedFileCounter.h"
 
 namespace aria2 {
 
@@ -226,8 +226,9 @@ void MultiDiskAdaptor::openIfNot
   if(!entry->isOpen()) {
         // A2_LOG_NOTICE(fmt("DiskWriterEntry: Cache MISS. offset=%s",
         //        util::itos(entry->getFileEntry()->getOffset()).c_str()));
-    if(getRequestGroupMan()) {
-      getRequestGroupMan()->ensureMaxOpenFileLimit(1);
+    auto& openedFileCounter = getOpenedFileCounter();
+    if(openedFileCounter) {
+      openedFileCounter->ensureMaxOpenFileLimit(1);
     }
     (entry->*open)();
     openedDiskWriterEntries_.push_back(entry);
@@ -278,8 +279,9 @@ void MultiDiskAdaptor::closeFile()
       dwent->closeFile();
     }
   }
-  if(getRequestGroupMan()) {
-    getRequestGroupMan()->reduceNumOfOpenedFile(n);
+  auto& openedFileCounter = getOpenedFileCounter();
+  if(openedFileCounter) {
+    openedFileCounter->reduceNumOfOpenedFile(n);
   }
 }
 
diff --git a/src/OpenedFileCounter.cc b/src/OpenedFileCounter.cc
new file mode 100644
index 00000000..c5bdeade
--- /dev/null
+++ b/src/OpenedFileCounter.cc
@@ -0,0 +1,100 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2014 Tatsuhiro Tsujikawa
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#include "OpenedFileCounter.h"
+
+#include <cassert>
+
+#include "RequestGroupMan.h"
+#include "RequestGroup.h"
+#include "PieceStorage.h"
+#include "DiskAdaptor.h"
+#include "SimpleRandomizer.h"
+
+namespace aria2 {
+
+OpenedFileCounter::OpenedFileCounter(RequestGroupMan* rgman,
+                                     size_t maxOpenFiles)
+  : rgman_(rgman),
+    maxOpenFiles_(maxOpenFiles),
+    numOpenFiles_(0)
+{}
+
+void OpenedFileCounter::ensureMaxOpenFileLimit(size_t numNewFiles)
+{
+  if(!rgman_) {
+    return;
+  }
+
+  if(numOpenFiles_ + numNewFiles <= maxOpenFiles_) {
+    numOpenFiles_ += numNewFiles;
+    return;
+  }
+  assert(numNewFiles <= maxOpenFiles_);
+  size_t numClose = numOpenFiles_ + numNewFiles - maxOpenFiles_;
+  size_t left = numClose;
+
+  auto requestGroups = rgman_->getRequestGroups();
+
+  auto mark = std::begin(requestGroups);
+  std::advance(mark,
+               SimpleRandomizer::getInstance()->
+               getRandomNumber(requestGroups.size()));
+  for(auto i = mark; i != std::end(requestGroups) && left > 0; ++i) {
+    left -= (*i)->getPieceStorage()->getDiskAdaptor()->tryCloseFile(left);
+  }
+  for(auto i = std::begin(requestGroups); i != mark && left > 0; ++i) {
+    left -= (*i)->getPieceStorage()->getDiskAdaptor()->tryCloseFile(left);
+  }
+  assert(left == 0);
+  numOpenFiles_ += numNewFiles - numClose;
+}
+
+void OpenedFileCounter::reduceNumOfOpenedFile(size_t numCloseFiles)
+{
+  if(!rgman_) {
+    return;
+  }
+
+  assert(numOpenFiles_ >= numCloseFiles);
+  numOpenFiles_ -= numCloseFiles;
+}
+
+void OpenedFileCounter::deactivate()
+{
+  rgman_ = nullptr;
+}
+
+} // namespace aria2
+
diff --git a/src/OpenedFileCounter.h b/src/OpenedFileCounter.h
new file mode 100644
index 00000000..960292b1
--- /dev/null
+++ b/src/OpenedFileCounter.h
@@ -0,0 +1,76 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2014 Tatsuhiro Tsujikawa
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#ifndef D_OPENED_FILE_COUNTER_H
+#define D_OPENED_FILE_COUNTER_H
+
+#include "common.h"
+
+namespace aria2 {
+
+class RequestGroupMan;
+
+class OpenedFileCounter {
+public:
+  OpenedFileCounter(RequestGroupMan* rgman, size_t maxOpenFiles);
+
+  // Keeps the number of open files under the global limit specified
+  // in the option.  The caller requests that |numNewFiles| files are
+  // going to be opened.  This function requires that |numNewFiles| is
+  // less than or equal to the limit.
+  //
+  // Currently the only download using MultiDiskAdaptor is affected by
+  // the global limit.
+  void ensureMaxOpenFileLimit(size_t numNewFiles);
+
+  // Reduces the number of open files managed by this object.
+  void reduceNumOfOpenedFile(size_t numCloseFiles);
+
+  void setMaxOpenFiles(size_t maxOpenFiles)
+  {
+    maxOpenFiles_ = maxOpenFiles;
+  }
+
+  // Deactivates this object.
+  void deactivate();
+
+private:
+  RequestGroupMan* rgman_;
+  size_t maxOpenFiles_;
+  size_t numOpenFiles_;
+};
+
+} // namespace aria2
+
+#endif // D_OPENED_FILE_COUNTER_H
diff --git a/src/RequestGroup.cc b/src/RequestGroup.cc
index 066e0f21..8a111ddf 100644
--- a/src/RequestGroup.cc
+++ b/src/RequestGroup.cc
@@ -593,7 +593,10 @@ void RequestGroup::initPieceStorage()
     tempPieceStorage = ps;
   }
   tempPieceStorage->initStorage();
-  tempPieceStorage->getDiskAdaptor()->setRequestGroupMan(requestGroupMan_);
+  if(requestGroupMan_) {
+    tempPieceStorage->getDiskAdaptor()->setOpenedFileCounter
+      (requestGroupMan_->getOpenedFileCounter());
+  }
   segmentMan_ = std::make_shared<SegmentMan>(downloadContext_, tempPieceStorage);
   pieceStorage_ = tempPieceStorage;
 }
diff --git a/src/RequestGroupMan.cc b/src/RequestGroupMan.cc
index 92c3b8c6..938f83e5 100644
--- a/src/RequestGroupMan.cc
+++ b/src/RequestGroupMan.cc
@@ -82,6 +82,7 @@
 #include "DiskAdaptor.h"
 #include "SimpleRandomizer.h"
 #include "array_fun.h"
+#include "OpenedFileCounter.h"
 #ifdef ENABLE_BITTORRENT
 #  include "bittorrent_helper.h"
 #endif // ENABLE_BITTORRENT
@@ -116,7 +117,8 @@ RequestGroupMan::RequestGroupMan
     removedLastErrorResult_(error_code::FINISHED),
     maxDownloadResult_(option->getAsInt(PREF_MAX_DOWNLOAD_RESULT)),
     wrDiskCache_(nullptr),
-    numOpenFile_(0),
+    openedFileCounter_(std::make_shared<OpenedFileCounter>
+                       (this, option->getAsInt(PREF_BT_MAX_OPEN_FILES))),
     numStoppedTotal_(0)
 {
   appendReservedGroup(reservedGroups_,
@@ -125,6 +127,7 @@ RequestGroupMan::RequestGroupMan
 
 RequestGroupMan::~RequestGroupMan()
 {
+  openedFileCounter_->deactivate();
   delete wrDiskCache_;
 }
 
@@ -964,34 +967,4 @@ void RequestGroupMan::initWrDiskCache()
   }
 }
 
-void RequestGroupMan::ensureMaxOpenFileLimit(size_t numNewFile)
-{
-  size_t max = option_->getAsInt(PREF_BT_MAX_OPEN_FILES);
-  if(numOpenFile_ + numNewFile <= max) {
-    numOpenFile_ += numNewFile;
-    return;
-  }
-  assert(numNewFile <= max);
-  size_t numClose = numOpenFile_ + numNewFile - max;
-  size_t left = numClose;
-  auto mark = std::begin(requestGroups_);
-  std::advance(mark,
-               SimpleRandomizer::getInstance()->
-               getRandomNumber(requestGroups_.size()));
-  for(auto i = mark; i != std::end(requestGroups_) && left > 0; ++i) {
-    left -= (*i)->getPieceStorage()->getDiskAdaptor()->tryCloseFile(left);
-  }
-  for(auto i = std::begin(requestGroups_); i != mark && left > 0; ++i) {
-    left -= (*i)->getPieceStorage()->getDiskAdaptor()->tryCloseFile(left);
-  }
-  assert(left == 0);
-  numOpenFile_ += numNewFile - numClose;
-}
-
-void RequestGroupMan::reduceNumOfOpenedFile(size_t numCloseFile)
-{
-  assert(numOpenFile_ >= numCloseFile);
-  numOpenFile_ -= numCloseFile;
-}
-
 } // namespace aria2
diff --git a/src/RequestGroupMan.h b/src/RequestGroupMan.h
index 773184e8..ecf9675d 100644
--- a/src/RequestGroupMan.h
+++ b/src/RequestGroupMan.h
@@ -60,6 +60,7 @@ class Option;
 class OutputFile;
 class UriListParser;
 class WrDiskCache;
+class OpenedFileCounter;
 
 typedef IndexedList<a2_gid_t,
                     std::shared_ptr<RequestGroup> > RequestGroupList;
@@ -104,7 +105,7 @@ private:
 
   WrDiskCache* wrDiskCache_;
 
-  size_t numOpenFile_;
+  std::shared_ptr<OpenedFileCounter> openedFileCounter_;
 
   // The number of stopped downloads so far in total, including
   // evicted DownloadResults.
@@ -356,17 +357,6 @@ public:
     return keepRunning_;
   }
 
-  // Keeps the number of open files under the global limit specified
-  // in the option. The caller requests that |numNewFile| files are
-  // going to be opened. This function requires that |numNewFile| is
-  // less than or equal to the limit.
-  //
-  // Currently the only download using MultiDiskAdaptor is affected by
-  // the global limit.
-  void ensureMaxOpenFileLimit(size_t numNewFile);
-  // Reduces the number of open files managed by this object.
-  void reduceNumOfOpenedFile(size_t numCloseFile);
-
   size_t getNumStoppedTotal() const
   {
     return numStoppedTotal_;
@@ -381,6 +371,11 @@ public:
   {
     return lastSessionHash_;
   }
+
+  const std::shared_ptr<OpenedFileCounter>& getOpenedFileCounter() const
+  {
+    return openedFileCounter_;
+  }
 };
 
 } // namespace aria2
diff --git a/src/RpcMethodImpl.cc b/src/RpcMethodImpl.cc
index d1a7df29..fd4c3d49 100644
--- a/src/RpcMethodImpl.cc
+++ b/src/RpcMethodImpl.cc
@@ -68,6 +68,7 @@
 #include "SessionSerializer.h"
 #include "MessageDigest.h"
 #include "message_digest_helper.h"
+#include "OpenedFileCounter.h"
 #ifdef ENABLE_BITTORRENT
 # include "bittorrent_helper.h"
 # include "BtRegistry.h"
@@ -1567,6 +1568,11 @@ void changeGlobalOption(const Option& option, DownloadEngine* e)
       // TODO no exception handling
     }
   }
+  if(option.defined(PREF_BT_MAX_OPEN_FILES)) {
+    auto& openedFileCounter = e->getRequestGroupMan()->getOpenedFileCounter();
+    openedFileCounter->setMaxOpenFiles
+      (option.getAsInt(PREF_BT_MAX_OPEN_FILES));
+  }
 }
 
 } // namespace aria2