An automatic clutch unit for vehicle use includes a slave cylinder to engage and disengage a friction clutch, an automatically operated hydraulic fluid feed mechanism to be operated by a pump, selectively connected with the slave cylinder, a manually operated hydraulic fluid feed mechanism to be operated by the action of a clutch pedal, selectively connected with the slave cylinder and a change-over cylinder having a piston pushed to one side of the cylinder by a spring, arranged among a hydraulic fluid pipeline of the manually operated hydraulic fluid feed mechanism, a hydraulic fluid pipeline of the automatically operated hydraulic fluid feed mechanism and a hydraulic fluid pipeline of the slave cylinder, wherein the piston side of the cylinder is connected with the hydraulic fluid pipeline of the manually operated hydraulic fluid feed mechanism, and the spring side of the cylinder is connected with the hydraulic fluid pipelines of the automatically operated hydraulic fluid feed mechanism and the slave cylinder, and hydraulic pressure generated by depressing the clutch pedal is transmitted to the slave cylinder when the piston of the change-over cylinder is moved.