Is it allowed to place ads that is not belong to Google adsense on the same page where adsense ads are..? Or you can place only google adsense on a certain page...?

i think other ads are against the rules, but id check their tos to make sure, before you put other ads on your site.

It used to be that you couldn't use any other contextual ads on the same page that you use AdSense, but Google changed their policy a few months ago. I believe the new policy is it's ok as long as it's clear that the other ads aren't AdSense. The need to look different enough so there's no mistaking them as AdSense.

It's in the AdSense TOS so if you read trough that you should find what is and isn't allowed.