PURPOSE: To minimize the stroke of a pneumatic piston and to make the opening and closing speed of a cylinder high and stable by moving vertically a frame body for rotating a press by the cam effect accompanied with the rotation thereof to actuate the greater part of die opening and closing and subjecting the die to main pressurization by a pneumatic pressure.

CONSTITUTION: Pressurization mechanisms 1 and body parts 5 for mounting die which are disposed in a number of pieces on a pitch circle are rotated by a driving device as shown by an arrow. A cam groove 3b having an ascending and descending shape is provided on the circumferential wall of the member 3a fixed and installed on the outside circumference of such frame body for rotating the press and a cam follower 4 provided to the mechanism 1 so as to move in contact therewith moves the mechanism 1 vertically as the cam is moved by the above-described rotation of the mechanism 1. A top die 2a is then moved vertically, by which the dies are opened and closed. When the dies are mostly closed and the die 2a is under pressure, said die is pressed to the lower die 2b by the actuation of a single acting pneumatic cylinder piston 8. The stroke 7 of the piston 8 is thus reduced and extremely small consumption of air is required.