It's a freewheel, and a nice one (Italian). Looks to be in good shape. It is an older freewheel (I'd guess early 80's at the newest, after that Regina made mostly 6-speed freewheels), but it could have been screwed onto a newer wheel with a freehub. You need a Regina freewheel removal tool. Park makes them. Your LBS will have one if they do repairs on older bikes.