that attaches the pedal arm to the bicycle?

I have an older Specialized Rockhopper FS and somehow this bolt worked its way loose and now my pedal arm is no longer attached to the bike. Anybody know where I can buy a replacement?

I haven't ridden my bike in over a year because I've been too lazy to track down the bolt. I found a couple new trails though, so it's time to get everything back together.


Thanks.