셀렉트(select) 박스에서 다중선택 한 아이템 다른 셀렉트 박스로 옮기기

<script language="JavaScript">
<!--
	function addItem(){
		var frm = document.form1;
		var cnt = frm.sel1.options.length;
		var cnt2 = 0;

		for (var i=0 ; i < cnt ; i++){
			if(frm.sel1.options[i].selected == true){
				frm.sel2.options.add(new Option(frm.sel1.options[i].text, frm.sel1.options[i].value));
				cnt2++;
			}
		}

		for (var i=0 ; i < cnt2 ; i++){
			frm.sel1.options.remove(frm.sel1.selectedIndex);
		}
	}

	function removeItem(){
		var frm = document.form1;
		var cnt = frm.sel2.options.length;
		var cnt2 = 0;

		for (var i=0 ; i < cnt ; i++){
			if(frm.sel2.options[i].selected == true){
				frm.sel1.options.add(new Option(frm.sel2.options[i].text, frm.sel2.options[i].value));
				cnt2++;
			}
		}

		for (var i=0 ; i < cnt2 ; i++){
			frm.sel2.options.remove(frm.sel2.selectedIndex);
		}
	}
//-->
</script>

<form name="form1" method="get" action="">
<table border="1" align="center">
	<tr>
	<td width="200">
		<select name="sel1" size="10" style="width:100%" multiple>
		<option value="1">야근이 없다면 회사는?</option>
		<option value="2">덜덜덜</option>
		<option value="3">지름신의 압박!</option>
		<option value="4">헐</option>
		<option value="5">메롱</option>
		<option value="6">superkts.pe.kr</option>
		<option value="7">착한 것들</option>
		</select>
	</td>
	<td width="30" align="center"><input type="button" value=" ▶ " onclick="addItem()"><br><br><input type="button" value=" ◀ " onclick="removeItem()"></td>
	<td width="200">
		<select name="sel2" size="10" style="width:100%" multiple></select>
	</td>
	</tr>

	<tr>
	<td align="center" colspan="3">다중 선택 이동 테스트</td>
	</tr>
</table>
</form>