function is_valid_email(text_id) {
   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
   var address = document.getElementById(text_id).value;
   if(reg.test(address) == false) {
	  return false;
	}
    else return true;
}