Abstract: A reciprocating pump comprises a plurality of parallel connected cylinder plunger arrangements and is driven via a cam mechanism (10) by means of a rotary driving device. In order to insure a constant discharge, the cam mechanism (10) comprises in the case where three cylinder plunger arrangements are employed, three plate cams (14) fixed on a common shaft (13) so that they are spaced 120.degree. apart from each other, and the displacement curve (a1;a2;a3) of each plate cam is designed such that the sum of the displacement per unit angle of rotation in the accelerating section and the displacement per corresponding unit angle of rotation in the decelerating section is equal to the displacement per unit angle of rotation in the uniform velocity section.