<form>
<input type="text" id="numcode" onkeypress="checkNumber" />
</form>
<br>

<script type="text/javascript">
function checkNumber(e)
{
  var e = e || window.event;
  if(e.ctrlKey||e.altKey)return;
  var c = e.charCode || e.keyCode;
  return ((c > 47) && (c < 58));
}

document.getElementById('numcode').onkeypress=checkNumber;
</script>