Boot camp priority problem on start-up

Hi,

I am using late 2012 macbook pro with i7 2.9 Ghz. but not retina display. Operating system is 10.8.2.

I needed to use windows 7, so I decided to boot camp my macbook.

I am successful to install win7, everything works correctly.

But when I shut down or restart my macbook it is automatically opening with windows.

When I choose the start-up disk from system preferences, There is nothing to choose, empty.

So everytime I have to open my mac with pressing the option key, it makes me crazy.

I verify and repair both disks from disk utility, but nothing has changed.

Do you guys, any suggestions to give?

Thanks,