PURPOSE: To relieve shocks applied to each work processed and the machinery therefore by varying the pressurization force by and by only upon setting of the minimum and maximum values of the pressurization force and the time for its increase.

CONSTITUTION: The difference in the setting values between the max. and min. of pressurization force setting devices 22, 23 is determined at a subtractor circuit, and the result is divided by a constant at a D/A converter circuit for determination of the minute unit rise voltage. Digital signals are emitted from a counter circuit according to clock pulses given by a clock signal generator circuit at a certain interval within the specified rising time, and the unit rise voltage is multiplied by the counts of these digital signals, the result being added at a subsequent adding circuit to the min. value setting voltage V1 on the abovementioned setting device 22, and the sum is converted into amperage at a V/I converter circuit to be supplied to an electro-pneumatic convertive regulator 2. The current supplied to this regulator 2 is controlled for proportional control of the pneumatic pressure from the output port 21, which will provide mild increase of the pressurization force given through an actuator.