Abstract: An oil circuit in which a meter-in circuit and a differential circuit are combined is disposed. Oil is supplied from a variable capacity pump in order to make a mold opening/closing control apparatus operate. A position instruction signal obtained by integrating a velocity instruction signal and a positional deviation of the displacement of the mold opening/closing control apparatus are obtained. A flow-rate instruction signal is set by the positional deviation. Then, a differential switching determining section receives the positional deviation and determines differential switching, following which a differential change-over valve switches between the meter-in circuit and the differential circuit. With a gain switching section connected to the differential switching determining section, the gain switching section switches between a pump gain for the meter-in circuit and a pump gain for the differential circuit. The above variable capacity pump is controlled by the switched pump gain.