PURPOSE: To improve the controllability of a cutoff valve by connecting an operating fluid feed passage, provided on the upstream side of the cutoff valve, to an operating fluid recovery means by a passage provided with a fixed throttle and a variable throttle, and setting pressure in this connecting passage as pilot pressure.

CONSTITUTION: A pilot pressure control device 48 is formed of a cutoff valve 46, a connecting passage 50 for connecting an operating fluid feed passage 20, provided on the upstream side of the cutoff valve 46, communicably to a reservoir 10, and a fixed throttle 52 and a variable throttle 54 provided at this passage 50. Pressure between the fixed throttle 52 and the variable throttle 54 is taken out as pilot pressure and fed to the cutoff valve 46. In this constitution, the pilot pressure can be controlled as the separate value from supply pressure within a range below supply pressure by the control of the variable throttle 54, so that the switching of the cutoff valve 46 can be controlled without changing supply pressure.