If I have 5 or more blogsite & I link exchange with each other (all blog topic is same). and If I use google adsense on every blogsite. Is this against google adsense TOS?
As far as I know, that's not against the TOS, although a quick email to Google might be able to confirm.
Linking within your blogs or getting links from outside through friends' blogs etc. is okay but selling / buying links is strictly prohibited and google has its own way to identify link sales and penalize those who indulge in it.
Definitive answer: No. It is not against Google Adsense TOS to use adsense on more than one site, even if you own them and they are linking to each other. To explain the other user's answer: buying links is looked down upon by Google but is unrelated to Google Adsense. You will only be penalized for buying from major link exchange sites (if google can figure it out) or if a fellow user reports your link purchase (though this tool has been used dishonestly to destroy competitors as well).