PURPOSE: To make it possible to form a clear stamped image at a correct position by installing stamping devices radially at equal intervals around a work and allowing the stamping devices to ram into the other simultaneously on the peripheral surface.

CONSTITUTION: A position for setting a work is determined using a centering tool and at the same time, a stamping member 61 is set at a position suited for the work W at a stamping holder 6. After that, a piston/ cylinder mechanism 2 is activated to allow a sliding plate 11 and, in turn, the stamping holder 6 to ascend and stop at an appropriate position. Under this state, the work W is deposited at a work setting position. After that, the sliding plate 11 and, in turn, the stamping holder 6 are allowed to descend by activating the oleo- pressure system piston cylinder mechanism 3 to any appropriate stop position. Further, prime mover members 4, 4 are caused to ascend instantaneously by activation of the oleo-pressure system piston/cylinder mechanism 3 to move driven members 5, 5 in an internal direction instantaneously. Thus stamping holders 6 are actuated and, in turn, stamping members 61 are caused to batter at the periphery of the work W and simultaneous stamping action with the stamping components takes place.