Should I agree to my supervisor's request to place him as first author of my paper? I published 3 papers as first author. Now, my supervisor requested me to place him as first author in my 4th paper. Should I agree to my supervisor's request to place him as first author of my paper? Is this ethically fair and legitimate? Is this only in my country? 

He has the contribution of proofreading the paper, advising me how to organize the paper and results, suggesting co-authors for the paper. He does not know the paper technically, however.
This is hard to give good advice about without a lot of context. What is ethical and what is done (in some fields) don't necessarily match up well. In some fields, an advisor is often a co-author - even first author. 

If the other person has made no contribution to the paper then, ethically, the request is wrong. But you may need to accede to it just out of personal protection. If the advisor has some influence or control over your future then you may be stuck, no matter the ethics. And you may have no effective way to counter it while preserving your future career. 

It isn't really a question of which country, though this sort of thing does vary by field. In situations in which the advisor funds a lab in which work is done it is pretty common. 

But, think about why he is asking. Think about whether it is really valid. But think most about how your long term career will be affected if you go along and if you resist. 

And note that having another paper on your CV is still a good thing, even if he is first author. And even if it isn't right.