PURPOSE: To provide a pressure releasing hydraulic circuit which can release automatically the pressure of a circuit, eliminates the need for a costly solenoid operated directional control valve and obviates burn of an electromagnetic coil by conducting the pressure of a pressure source as a pilot pressure to a pilot check valve when a selector valve is in a neutral position.

CONSTITUTION: The solenoid 25b of a directional control valve 25 is conducted upon driving of a variable capacity type pump 43 to bring the valve 25 to a switching position V2. Hydraulic fluid is then supplied to the head side port 22a of a hydraulic cylinder 22 to advance the piston rod 22c of a cylinder 22, thereby pressing a movable plate 21 toward a master plate. When the filter plate between the master plate and the plate 21 is locked and the pressure of a load line 23 attains a specified value or above, the operation of the pump 43 is stopped by the output from a pressure switch 39 which turns on. The solenoid 25b of the valve 25 is turned on in this state to reset the valve 25 to a neutral position V0. The pump 43 is then driven to open a pilot check valve 35 so that the hydraulic fluid on the head side of the cylinder 22 is discharged to a tank 32, by which the pressure is automatically released. The cake between the filter plates is at the same time expanded. A restrictor 33 prevents the abrupt discharge of the hydraulic fluid to the tank 32.