To provide a reciprocating pump unit which can easily and skillfully perform, even in case of a narrow width in a cylinder of a pump, adjusting operation of delivery amount of a delivery amount adjusting mechanism having a limiting member for adjusting the delivery amount by changing the stroke of a piston.

A plurality of sets of reciprocating pumps 20 are stacked in a laterally arranged direction S relating to a reciprocating direction R of a piston rod, to additionally arrange a delivery amount adjusting mechanism 40 for individually adjusting a delivery amount in each reciprocating pump, the respective delivery amount adjusting mechanism comprises a limiting member for limiting an energizing movement position by an energizing member of the piston rod and a limiting position adjusting means 13, 45 for adjusting a position of the limiting member, and the limiting member and the limiting position adjusting means are arranged in a front side F of a plurality of sets of the reciprocating pumps.