PURPOSE: To stiffen the mechanism of a clutch control device, and reduce the price by combining the hydraulic system of a master cylinder with the hydraulic system of a sub master cylinder of the clutch control device by a three-port valve, and integrating a release cylinder to simplify the mechanism of the clutch control device.

CONSTITUTION: A clutch 1 is controlled by using a three-port valve 20 to switch the hydraulic systems 4, 9 of a master cylinder and the hydraulic systems 11, 15 of a clutch control device to integrate a release cylinder 3. When the hydraulic system is switched, the oil amount is kept constant so as to prevent the transfer of the oil to/from each other.