PURPOSE: To perform maintenance-free operation throughout a long time, by surrounding the peripheral surface of a plunger with a space, forming the space between a pair of seals neighboring to a delivery metering chamber and filling detergent liquid in said space.

CONSTITUTION: Constitution is such that a space 7, surrounding the peripheral surface of a plunger 8, is formed neighboring to a delivery metering chamber 10 between a pair of seals 49, 49 slidably contacted to the plunger 8, and detergent liquid is filled into said space 7 from a wet cup 6. In this way, damage of the plunger 8 or the seal 49, caused by solidification or the like of metered and delivered liquid contacted to air, can be prevented, and maintenance-free operation can be performed for a long time.