PURPOSE: To obtain quick characteristic pressure resin in spite of using simple and small rating of hydraulic system by communicating a front part oil chamber and a rear part oil chamber in a die clamping cylinder with a differential circuit.

CONSTITUTION: At the time of die clamping, by changing over a change-over valves 39, 41 in the differential circuit 30 so that logic valves 35, 38 open by hydraulic pressure in hydraulic passage 34 side, working oil in the rear part oil chamber 32 is shifted to the front part oil chamber 3 according to shifting of a die champing piston 11, and the excessive working oil generated from the difference between the pressure receiving areas is discharged into a tank as drain. Chucking at the tip part of tie bar 9 with the chuck 22 is sensed by a limit switch, and at the time of confirming completion of die closing the change-over valve 39 in the differential circuit 30 is changed over so that the logic valve 35 closes by circuit pressure at the front part oil chamber side. Two oil chambers are made to the shutting-off condition, but the rear part oil chamber is under the communicating condition with the tank and the working oil from a pump side circuit 36 is supplied only to the front part oil chamber 31 to execute the high pressure die clamping.