POSITIVE DISPLACEMENT FLOWMETER

[OBJECT] To provide a volumetric flow meter capable of easily performing bubble removing without high pump pressure.[MEANS OF REALIZING THE OBJECT] A volumetric flow meter 1 including: a piston rod 24 including pistons 22, 23 at both ends; cylinders 25, 26 for accommodating the pistons mounted on the both ends of the piston rod; cylinder chambers 21f, 21g drilled on a main body 21, the cylinder chambers separately accommodating the cylinders; passages 21d, 21e separately opening near cylinder chambers outside the cylinders to separately communicate with both cylinder chambers, and being alternately switched to an inflow passage and an outflow passage by a switching valve 17; and piston covers 29, 30 separately opposing to the cylinder chambers and the passages, wherein convex parts 30b are separately formed on inner surfaces of the piston covers or portions of the main body opposing to the inner surfaces of the piston covers.