How to redirect to a perticualr page if access denied.....

 Hi
 
I am using roles in my website,
 
I have "admin" sub folder in my project folder.
If any user without "admin" roles tries to access "admin" pages, its redirecting to the "Login" page.
 
What I want is, instead it should redirect to a custom Page, which will show my text or show access denied info.
 
More info:
Inside the "admin" folder "web.config" is there, it contains:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <system.web>
        <authorization>
            <allow roles="admin" />
    & ...