<html>
<body>
<form>
<div id=divf>
<input type=text>
</div>
<input type=button onclick=plus()>
</form>
<script>
var n=0
function plus(){
document.getElementById('divf').innerHTML+='<br><input type=text id="id'+n+'" name="name'+n+'">'
n++
}
</script>
</body>
</html>