the engaged position to the disengaged position is detected in step 02 a check is performed to confirm whether the pto lever 17 has been moved to the disengaged position or to an area regarded as the disengaged position 08 when the pto lever 17 has been moved to the disengaged position or to the area regarded as the disengaged position u201c yes u201d branch of 08 the actuating pressure p of the pto clutch 6 is reduced according to the previously set high speed control characteristics and a disengaging process for switching the pto clutch 6 to the disengaged state is performed regardless of the operating speed 09 the control reference speed v 1 can be switched between high speed and low speed by operating the setting switch 18 when the control reference speed v 1 is switched to high speed then as long as the pto lever 17 is not moved at a fairly high speed from the disengaged position to the engaged position the process will not diverge to step 06 after the check performed in step 04 it is therefore possible to control the actuating pressure p of the pto clutch 6 harmonized with the speed at which the pto lever 17 is operated this control is suitable when comparatively small sized implements.