PURPOSE: To permit maximum force to be exerted within a range not to burn a motor at all times, by moving a cylinder by means of a trigger in accordance with a discharging load condition of fluidic member fed back in such a manner that its feedback condition is felt by a hand actually.

CONSTITUTION: When supply of fluidic member begins, a cylinder 46 is set at a position where it can produces a maximum discharge pressure in relation to a plunger 33 to cope with a highly loaded condition of the fluidic member to be fed under pressure. Then, a trigger 61 is pulled to a position where it can be operated easily when a load fed back to a hand by pulling the trigger 61 is small. The pulling action causes the cylinder 46 to move to a direction to deepen a maximum plunging position of the plunger 33 so that a state of high pressure and small discharge amount shifts to a state of low pressure and large discharge amount. With this arrangement, a target value in the case that the cylinder is controlled manually becomes a optimum maximum motor load for permitting a motor to perform a maximum job at all times within a range it is not burnt.