diff --git a/ChangeLog b/ChangeLog
index 94027d8f73..61874afbb2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun May 23 17:29:41 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* common.mk (capi): uses a timestamp file to get rid of 
+	  generating twice.
+
 Fri Jun 18 01:33:21 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
 
 	* enc/Makefile.in (realclean): has been missing. necessary
diff --git a/common.mk b/common.mk
index 6cfb0fbd6e..47b6658e75 100644
--- a/common.mk
+++ b/common.mk
@@ -148,9 +148,11 @@ miniruby$(EXEEXT): config.status $(NORMALMAINOBJ) $(MINIOBJS) $(COMMONOBJS) $(DM
 GORUBY = go$(RUBY_INSTALL_NAME)
 golf: $(LIBRUBY) $(GOLFOBJS) PHONY
 	$(MAKE) $(MFLAGS) MAINOBJ="$(GOLFOBJS)" PROGRAM=$(GORUBY)$(EXEEXT) program
-capi: Doxyfile PHONY $(PREP)
+capi: doc/capi/.timestamp PHONY
+doc/capi/.timestamp: Doxyfile $(PREP) 
 	@$(MAKEDIRS) doc/capi
 	@$(DOXYGEN) -b
+	$(MINIRUBY) -e 'File.open("doc/capi/.timestamp", "w"){|f| f.puts(Time.now)}'
 
 Doxyfile: $(srcdir)/template/Doxyfile.tmpl $(PREP) $(srcdir)/tool/generic_erb.rb $(RBCONFIG)
 	$(MINIRUBY) $(srcdir)/tool/generic_erb.rb -o $@ $(srcdir)/template/Doxyfile.tmpl \