添加页码以在wordpress主题上发布

I am building custom theme. If I have got long post (like review, tutorial) I would like to cut this post for 5 parts. I would love to make navigation at the bottom of post. So, I have added this code to post, but it does not show navigation:

<!--nextpage-->

So, I have added this in the place of single.php, but it also does not show this:

<?php wp_link_pages(); ?>

How to add this element?

OK, I got it. It is very simple...

<?php wp_link_pages(); ?>

Shoud be in the loop...