A reciprocating pump is provided that does not leak working liquid to the exterior. A communicating tube 14 extends over both a first manifold 4 and a second manifold 5 such that a reciprocating member 1 constitutes a part of a reciprocating cylinder 2. An auxiliary O-ring 24 is disposed on connection surfaces 13a and 13b of a first manifold 4 and a second manifold 5 outside of the communicating tube 14 in the radial direction so that liquid leaking from at least one of a first O-ring 15 between the first manifold 4 and the periphery of the communicating tube 14 and a second O-ring 16 between the second manifold 5 and the periphery of the communicating tube 14 toward the exterior is blocked.