PURPOSE: To enable a vehicle such as a truck to make a smooth starting operation, by putting a hydraulic pressure of the clutch to zero in a state where a stem is stretched in a full stroke, and enabling the clutch to be in engagement while at the same time non-linearly increasing the hydraulic pressure by return stroke of the stem.
CONSTITUTION: When a stem 2 is pulled up and a gear shift lever is switched, starting operation a switch valve 22 is shifted to the left position 22b, then a hydraulic pressure at a pilot port 20 flows to a tank port T after passing a chamber 21, the hydraulic pressure from an inlet port 13 flows to an outlet port 12. When a clutch fluid pressure in a liquid chamber 18 increases, in such a state a pilot spool 14 lifts a main spool 9, communication between the ports 12, 13 is shut off and hydraulic pressure of the starting clutch 23 is maintained at zero. Then, if the stem 2 is returned, a contraction of the area leading to the outlet port 12 is formed by downward movement of spools 9, 14. Then, as the tank port is closed, the ports 12, 13 come to communicate with each other, to allow engagement of the clutch 23.