How to add “Leave a comment” link to post pages?

Hullo,
I use <?php comments_popup_link(); ?> to add “Leave a comment” link at the bottom of each post on my front page (you can see it on my blog). But this does not work for my single post pages. I understand it does not have to be, because the commenting window is automatically attached to post pages. But if I want the comment link to show anyway, how do I do it?
Thanks.