diff --git a/bin/git-sync b/bin/git-sync
index 765f19a..cbb6845 100755
--- a/bin/git-sync
+++ b/bin/git-sync
@@ -5,14 +5,19 @@ function _usage()
   local command="git sync"
   cat << EOS
 Usage:
-  ${command} <remote> <branch>
-  ${command} -h | --help | help | ?
+  ${command} [<remote> <branch>]
+  ${command} -h | --help
 
-Sync local branch with <branch> of <remote>.
+Sync local branch with <remote>/<branch>.
+When <remote> and <branch> are not specified on the command line, upstream of local branch will be used by default.
 All changes and untracked files and directories will be removed.
 
-Example:
-  ${command} origin master
+Examples:
+  Sync with upstream of local branch:
+    ${command}
+
+  Sync with origin/master:
+    ${command} origin master
 EOS
 }
 
@@ -20,8 +25,9 @@ function main()
 {
   while [ "$1" != "" ]; do
     case $1 in
-      -h | --help | help | "?" )
+      -h | --help)
         _usage
+        exit
         ;;
       * )
         if [ "${remote}" = "" ]; then
@@ -38,18 +44,24 @@ function main()
     shift
   done
 
-  if [ "${remote}" = "" -o "${branch}" = "" ]; then
-     echo -e "Error: too few arguments.\n"
-     _usage
-     exit 1
+  if [ "${remote}" = "" ]; then
+    local remote_branch="$(git rev-parse --abbrev-ref --symbolic-full-name @{u})"
+    branch="$(git rev-parse --abbrev-ref --symbolic-full-name @)"
+    remote="${remote_branch%%/${branch}}"
+  elif [ "${branch}" = "" ]; then
+    echo -e "Error: too few arguments.\n"
+    _usage
+    exit 1
+  else
+    local remote_branch="${remote}/${branch}"
   fi
 
-  echo "Are you sure you want to clean all changes & sync with '${remote}/${branch}'? [y/N]"
+  echo "Are you sure you want to clean all changes & sync with '${remote_branch}'? [y/N]"
   local res
   read res
-  case ${res} in
+  case "${res}" in
     "Y" | "y" | "yes" | "Yes" | "YES" )
-      git fetch '${remote}' && git reset --hard '${remote}'/'${branch}' && git clean -d -f -x
+      echo "git fetch "${remote}" "${branch}" && git reset --hard "${remote_branch}" && git clean -d -f -x"
       ;;
     * )
       echo "Canceled."
diff --git a/man/git-sync.1 b/man/git-sync.1
index 90a4954..498b2f2 100644
--- a/man/git-sync.1
+++ b/man/git-sync.1
@@ -7,12 +7,31 @@
 \fBgit\-sync\fR \- Sync local branch with remote branch
 .
 .SH "SYNOPSIS"
-\fBgit sync\fR <remote> <branch>
+\fBgit sync\fR [ <remote> <branch> ]
 .
 .SH "DESCRIPTION"
-Sync local branch with <branch> of <remote>\. All changes and untracked files and directories will be removed\.
+Sync local branch with <remote>/<branch>\.
+.
+.P
+When <remote> and <branch> are not specified on the command line, upstream of local branch will be used by default\.
+.
+.P
+All changes and untracked files and directories will be removed\.
 .
 .SH "EXAMPLES"
+Sync local branch with its upstream
+.
+.IP "" 4
+.
+.nf
+
+$ git sync
+.
+.fi
+.
+.IP "" 0
+.
+.P
 Sync local branch with origin/master
 .
 .IP "" 4
diff --git a/man/git-sync.html b/man/git-sync.html
index 05a5c1f..234cdb0 100644
--- a/man/git-sync.html
+++ b/man/git-sync.html
@@ -75,15 +75,23 @@
 
 <h2 id="SYNOPSIS">SYNOPSIS</h2>
 
-<p>  <code>git sync</code> &lt;remote&gt; &lt;branch&gt;</p>
+<p>  <code>git sync</code> [ &lt;remote&gt; &lt;branch&gt; ]</p>
 
 <h2 id="DESCRIPTION">DESCRIPTION</h2>
 
-<p>  Sync local branch with &lt;branch&gt; of &lt;remote&gt;.
-  All changes and untracked files and directories will be removed.</p>
+<p>  Sync local branch with &lt;remote&gt;/&lt;branch&gt;.</p>
+
+<p>  When &lt;remote&gt; and &lt;branch&gt; are not specified on the command line, upstream of local branch will be used by default.</p>
+
+<p>  All changes and untracked files and directories will be removed.</p>
 
 <h2 id="EXAMPLES">EXAMPLES</h2>
 
+<p>  Sync local branch with its upstream</p>
+
+<pre><code>$ git sync
+</code></pre>
+
 <p>  Sync local branch with origin/master</p>
 
 <pre><code>$ git sync origin master
@@ -91,7 +99,7 @@
 
 <h2 id="AUTHOR">AUTHOR</h2>
 
-<p>Written by Takuma Yamaguchi &lt;<a href="&#109;&#x61;&#x69;&#108;&#116;&#111;&#58;&#107;&#x75;&#109;&#111;&#x6e;&#x30;&#53;&#56;&#55;&#64;&#103;&#x6d;&#97;&#105;&#108;&#x2e;&#99;&#x6f;&#109;" data-bare-link="true">&#107;&#117;&#x6d;&#x6f;&#110;&#x30;&#53;&#x38;&#55;&#64;&#x67;&#109;&#97;&#x69;&#108;&#x2e;&#99;&#x6f;&#x6d;</a>&gt;</p>
+<p>Written by Takuma Yamaguchi &lt;<a href="&#x6d;&#97;&#x69;&#x6c;&#116;&#x6f;&#x3a;&#107;&#x75;&#109;&#x6f;&#x6e;&#x30;&#53;&#56;&#55;&#64;&#x67;&#x6d;&#97;&#105;&#108;&#x2e;&#99;&#111;&#109;" data-bare-link="true">&#107;&#117;&#109;&#x6f;&#110;&#48;&#x35;&#x38;&#x37;&#64;&#103;&#109;&#97;&#105;&#108;&#x2e;&#x63;&#111;&#x6d;</a>&gt;</p>
 
 <h2 id="REPORTING-BUGS">REPORTING BUGS</h2>
 
diff --git a/man/git-sync.md b/man/git-sync.md
index 8854634..f2f6e43 100644
--- a/man/git-sync.md
+++ b/man/git-sync.md
@@ -3,15 +3,22 @@ git-sync(1) -- Sync local branch with remote branch
 
 ## SYNOPSIS
 
-  `git sync` &lt;remote&gt; &lt;branch&gt;
+  `git sync` [ &lt;remote&gt; &lt;branch&gt; ]
 
 ## DESCRIPTION
 
-  Sync local branch with &lt;branch&gt; of &lt;remote&gt;.
+  Sync local branch with &lt;remote&gt;/&lt;branch&gt;.
+  
+  When &lt;remote&gt; and &lt;branch&gt; are not specified on the command line, upstream of local branch will be used by default.
+  
   All changes and untracked files and directories will be removed.
 
 ## EXAMPLES
 
+  Sync local branch with its upstream
+
+    $ git sync
+
   Sync local branch with origin/master
 
     $ git sync origin master
@@ -27,4 +34,3 @@ Written by Takuma Yamaguchi &lt;<kumon0587@gmail.com>&gt;
 ## SEE ALSO
 
 &lt;<https://github.com/tj/git-extras>&gt;
-