如何在WordPress内容上显示html？

I have a custom WordPress theme where user can post. I use the WP Editor (only text mode) to write the content, and then on the post page i Show the content calling the_content(); function. But then when I'm going to see the post it shows the html code.. Look: (the content is the text inside the blue div)

How can I show the text in bold for example? :S I tried also to put but the result is the same.. Mi code where i call the content is this:

<div class="content_"><?php the_content(); ?></div>

I don't know why it is showing the html code..