To contemplate the connection of a nozzle part supporting a cover body to a body part accurately as well as its disconnection from this body part easily, respectively.

An engaging hole 16 of a piston 5 and an engaging projection 17 of a nozzle part 7 are aligned up and down, and when a connecting part 10 of a nozzle holder 9 is inserted into a tip part of the piston 5, an incline on an underside of the engaging projection 17 comes into contact with an inner edge of the tip of the piston 5, pressing this inner edge outward. In a coincidence of two positions of the engaging projection 17 and the engaging hole 16, a part 5a of the tip part of the piston 5 is put back to the original position and the nozzle part 7 is connected to the tip part of the piston 5. As to removal, a cover part 13 is rotated counterclockwise and the incline of the engaging projection 17 presses an edge of the engaging hole 16 of the piston 5 outwards, and when the nozzle part 7 is pulled upward at a position where the engaging hole 16 is none, positive mounting and easy removal both are achievable.