PURPOSE: To implement a smooth control for controlling a plurality of solenoid selector valves by setting the opening time of each solenoid selector valve for a train of a plurality of unit width pulses and shifting a rise position of the unit width pulses of an arbitrary solenoid selector valve for that of the other solenoid selector valve.

CONSTITUTION: In a hydraulic cylinder 1 for vibrating a mold of a continuous casting facility, a plurality of solenoid selector valves, for example, four valves 4 (4A-4D) are disposed on each hydraulic pipe 3 discharging oil from both cylinder rooms 2 thereof, respectively. In a hydraulic pressure control of a driving unit like this, opening time of each selector valve 4 is made a pules train combining a plurality of unit width pulses (pulse period: ts) and a rise position of the unit width pulse is set in each selector valve 4 so as to be alternately shifted by a half period of the unit width pulse (ts/2). This smoothly changes a quantity of oil discharged from the hydraulic cylinder 1 to improve the accuracy of control.