PURPOSE: To improve startability in the stage of clutch engagement and to reduce the time until stable operation is attained by connecting two pipelines for fluid pressure to a piston chamber thereby assuring braking performance.

CONSTITUTION: A high pressure pipeline 23 and a low pressure pipeline 19 are opened to supply an air pressure to a piston and to move quickly the piston to a drive plate side and to bring the same into press contact with the drive plate thereby starting a crank shaft in the stage of starting operation. Both pipelines 19, 23 are closed thereafter to stop the operation of the machine base so that the piston is brought into press contact with the brake plate by the return pressure of a spring to stop the inertia rotation of the crank shaft. Only the pipeline 19 is again opened so that the machine stands by to be ready for restarting the operation. The spring having the intensified return pressure is adopted for the above-mentioned purpose to assure the breaking performance. The effective pressing force of the piston against the drive plate side in the stage of starting operation is increased and the required rise time is reduced.