Abstract: A plunger pump wherein a bellows is provided between the plunger and the plunger case to thereby protect a slide surface of the plunger from a pressure-fed fluid such as inorganic paint, zinc rich paint.In this plunger pump, the pressure-fed fluid is allowed to flow between the outer surface of the bellows and the inner surface of the plunger case, only the removal of the plunger after use can expose the outer surface of the bellows so as to facilitate removing the pressure-fed fluid such as the coating composition including paint and cleaning the bellows, and moreover, the effective diameter of the bellows is made equal in value to the outer diameter of a portion, which is slidable on the plunger case and projected into a portion communicated with the interior of the bellows so as to eliminate an occurrence of an unusual deformation of the bellows.