PURPOSE: To improve oscillation resistance and reliability by inserting an auto matic change-over valve into a space between a control valve and an arm opening or closing hydraulic cylinder, and by providing a circuit for pressure oil to be fed to, with a check valve for detecting the reduction or stop of the flow of the pressure oil, and a throttle valve.

CONSTITUTION: When a control valve 8 is switched to the closing position of an opening or closing arm, then pressure oil from a hydraulic source 7 is infiltrated into the head chamber (a) of a hydraulic cylinder 6 via the control valve 8, a pilot check valve 10, and an automatic change-over valve 9, and the opening or closing valve is worked in the closing direction. After that, when the hydraulic cylinder 6 comes to a stroke end or the elongation of the hydraulic cylinder 6 is stopped, then the flow rate of a circuit 11 is extremely reduced or comes to zero, and the opening or closing arm starts opening- working. When the pressure oil flows to the pilot check valve 10 by the switching of the automatic change-over valve 9 to the right position, then differential pressure is generated on the pilot check valve 10, and the automatic change-over valve 9 is reset to the left position.