To relax a trangent in switching to a mechanical back up mode and to ensure a predetermined actuator speed in the mechanical back up mode.

A restriction means 40 which can restrict a switching speed of a directional control valve 33 is provided on an oil passage for imparting a switching operation pressure Pa to the mode directional control valve 33 when the mode directional control valve 33 is switched such that a mechanical control valve 31 is inserted to a feeding/discharging passage of an operation oil to an actuator 10. When the mode directional control valve 33 inserts the mechanical control valve 31 to the feeding/discharging passage of the operation oil to the actuator 10 by a predetermined variation of the switching operation pressure Pa, a restriction means 40 is operated by a switching operation pressure variation. Thereby, an operation oil feeding/discharging control is temporarily restricted by the mechanical control valve 31 inserted to the operation oil feeding/discharging passage.