You really have to be strong and keep putting him back in his cot. It'll probably cause a few nights of sleeplessness but, trust me, it's so worth it!
Babies are alot smarter than we give them credit for. He'll cry because he know's you'll take him into bed with you, not because there's anything wrong with his cot. Put him down to bed as normal and when he wakes in the night, give him a quick cuddle and put him back into bed. No matter how many time you need to do this, don't give in.
The older he is the harder it will be. My son was in my bed until he turned 9 months and one night I spend 5-6 hours getting him back to sleep but he's been a great sleeper since. I was so determined to do it because my hubby was in with his parents until he was 4, I couldn't cope with that lol.
Good luck, don't leave it any longer or it will just get harder and harder to do xxx