Insert Statement Executing Repeateadly On The Page Refresh

i have a form that action is set to itself, on the same page i m having the insert statement, executed when i submit that form, but when the user refresh that page the query is executed and submit the null values in the table.

<form name=form1 action=form1.asp method=post>
<input type........
<input type.......

<input type=submit value....>
<input type=hidden name='insert' value=1>
</form>

<%
if request.form("insert") = 1 then

Execute the insert query

End If

%>