PLUNGER PUMP

PROBLEM TO BE SOLVED: To provide a plunger pump capable of discharging liquid with high accuracy even when a discharge amount is minute. SOLUTION: The plunger pump 1 is provided with a cylinder 7 having a discharge port 3 and a suction port 5, and a plunger 11 structured on an insertion port 9 formed on the cylinder 7 so as to slidably reciprocate, discharges the liquid from the discharge port 3 when a volume of the sealed cylinder 7 shrinks, and sucks the liquid from the suction port 5 when the volume of the sealed cylinder 7 enlarges in accordance with reciprocation of the plunger 11. The cylinder 7 is provided with an engaging port 19 which can slidably reciprocate in a state that a tip end part of the plunger 11 is engaged, and the insertion port 9 and the engaging port 19 have different opening cross sectional areas. The plunger pump 1 can discharge the liquid of a minute amount with high accuracy as compared with a conventional example.