\pagestyle{empty} doesn't work on first page of new chapter

I have a problem with page numbering in LaTeX. I don't want any page number in my document so I used \pagestyle{empty} but every time when I start a new chapter I get a page number on the bottom center of the page with the chapter's title. What should I do to remove those page numbers?

My document class looks like this:

\documentclass[12pt, a4paper]{book}