PURPOSE: To improve considerably the workability when a die engaging part is attached or detached to or from a die in such constitution wherein the die engaging part approaches the die when the piston rod of the 1st cylinder extends and that the die engaging part clamps the die when the piston rod of the 2nd cylinder rotates.

CONSTITUTION: Solenoid valves 39, 40 are changed over by a command for clamping to connect ports 29, 30 to a tank 44 and a port 31 to a pump 37 in the case of clamping a die 15 with a die engaging part 2. A piston 10 is therefore moved upward by an oil pressure. When the piston 10 arrives at the uppermost position, the part 2 is positioned upper than the top surface in the edge part of the die 15. Solenoid valves 38, 40 are then changed over to connect the ports 30, 31 to the tank 44 and the port 29 to the pump 37. A rack 4 is therefore moved leftward by the oil pressure, and a piston rod 11 rotates 90° accordingly. The flat die engaging part 2 having a T shape is then rotated to the position where it is engaged with the die 15 and the die 15 is thus clamped.