To miniaturize a return spring which converts the swinging motion of a trigger to the ascending/descending motion of a piston and at the same time, returns the trigger into a direction in which it is initially positioned by molding the return spring of a plastic material in a laterally almost arc fashion so that the return spring is elastically deformable in a stretchable direction.

The pulling of a trigger 12 enables the rotation of a pinion 48 following the rotation of a sector gear 46 and consequently, the descending of a piston 16 through a rack 44. In turn, a liquid contained in a cylinder 14 is pressurized and the pressurized liquid is jetted from the orifice 24 of a nozzle 22 through a secondary valve 38. In this case, the base piece 50a of a return spring 50 molded of a plastic material in a laterally almost L form is pulled downward resulting in the elastic deformation of the return spring 50. Thus a restoring force to return the return spring 50 to its original shape is generated on the spring 50 by the elastic deformation. Further, the piston 16 is caused to ascend by the restoring force when the traction force of the trigger 12 is relieved, and the liquid contained in a container 18 is sucked into the cylinder 14 through a primary valve 36.