To realize the automatic exchange of dies by turnably providing a hollow worm wheel in a die supporting member of a punch press, providing a key groove in the die, and providing a positioning pin to be engaged with the key groove of the dies thereby simplifying an auto-index mechanism.

An air cylinder 65 is operated, a positioning pin 49 is engaged with a key groove 19 provided in a retainer collar 17 to stop the rotation of a punch body 37 and obtain the position of a striking part 47. A die holder 13 is turned. A large number of punches 21 are arranged in the circumferential direction of the die holder 13, and an upper part of a T-shaped groove 37T of only one of the punches in the die holder 13 is hollow to form the striking part, and the upper parts of other T-shaped grooves 37T are void, i.e., forming punch through holes 45. The lowering movement of a striker 5 lowers a punch head 53, a punch driver 41, and a punch body 37, only a punch blade tip part 29 at the tip of a punch 21F below the hollow striking part 47 is lowered while other punches are retreated in the space of the punch through holes 45, and not lowered.