diff --git a/include/mcl/fp_util.hpp b/include/mcl/conversion.hpp
similarity index 99%
rename from include/mcl/fp_util.hpp
rename to include/mcl/conversion.hpp
index 7712e9c..6fbd394 100644
--- a/include/mcl/fp_util.hpp
+++ b/include/mcl/conversion.hpp
@@ -2,7 +2,7 @@
 #include <vector>
 #include <cybozu/itoa.hpp>
 #include <cybozu/atoi.hpp>
-#include <mcl/unit.hpp>
+#include <mcl/util.hpp>
 /**
 	@file
 	@brief utility of Fp
diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index f10fe14..43e8a1b 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -20,10 +20,8 @@
 //	#define USE_MONT_FP
 #endif
 #include <cybozu/hash.hpp>
-#include <cybozu/itoa.hpp>
-#include <cybozu/atoi.hpp>
 #include <mcl/op.hpp>
-#include <mcl/unit.hpp>
+#include <mcl/util.hpp>
 #include <mcl/power.hpp>
 
 namespace mcl {
diff --git a/include/mcl/unit.hpp b/include/mcl/util.hpp
similarity index 100%
rename from include/mcl/unit.hpp
rename to include/mcl/util.hpp
diff --git a/src/fp.cpp b/src/fp.cpp
index 77af38f..4ddaa5d 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -1,6 +1,6 @@
 #include <mcl/op.hpp>
-#include <mcl/unit.hpp>
-#include <mcl/fp_util.hpp>
+#include <mcl/util.hpp>
+#include <mcl/conversion.hpp>
 #ifdef USE_MONT_FP
 #include <mcl/fp_generator.hpp>
 #endif
diff --git a/test/base_test.cpp b/test/base_test.cpp
index d78364a..5e0d378 100644
--- a/test/base_test.cpp
+++ b/test/base_test.cpp
@@ -5,7 +5,7 @@
 #include <cybozu/benchmark.hpp>
 #include <cybozu/xorshift.hpp>
 #include <cybozu/bit_operation.hpp>
-#include <mcl/fp_util.hpp>
+#include <mcl/conversion.hpp>
 #include <mcl/fp.hpp>
 
 #include <mcl/fp_generator.hpp>
diff --git a/test/fp_util_test.cpp b/test/fp_util_test.cpp
index c9785ab..d32587f 100644
--- a/test/fp_util_test.cpp
+++ b/test/fp_util_test.cpp
@@ -1,5 +1,5 @@
 #define PUT(x) std::cout << #x "=" << (x) << std::endl
-#include <mcl/fp_util.hpp>
+#include <mcl/conversion.hpp>
 #include <cybozu/test.hpp>
 
 CYBOZU_TEST_AUTO(toStr16)