Abstract: The present invention allows an operating device to be driven by power taken from an input shaft of a mechanical speed change gear. A clutch interposed between the power take-off shaft and the operating device automatically disengages when gears are being shifted to prevent the inertial rotation of the operating device from being transmitted to the input shaft during gear shifts. The inertial rotation would otherwise hinder the gear shifting operation by driving the input shaft even though the engine is disengaged by a main clutch. Inertial rotation is of special concern when synchromesh gears are used in the transmission, because it inhibits synchronization, resulting in large probability of abnormal wear to the synchronizer rings or a breakdown of clutch teeth. The present invention solves the problem of inertial rotation being transmitted from the operating device to the input shaft during the gear shifting process.