Thank you so much for reply.
Its working fine, for reference i have include below code.
<system.webServer>
<httpErrors existingResponse="Replace" errorMode="Custom">
<remove statusCode="403"/>
<remove statusCode="404"/>
<error statusCode="403" path="../CustomErrorPage.aspx" responseMode="Redirect" />
<error statusCode="404" path="../CustomErrorPage.aspx" responseMode="Redirect" />
</httpErrors>
</system.webServer>
Below are customerrorpage.aspx.cs file
protected void Page_Load(object sender, EventArgs e)
{
Response.Redirect("~/404.htm", true);
}