To further reduce the minute vibration of pressure wave of the water discharged in a plunger pump, and to provide a simple, inexpensive constitution for the plunger pump requiring a small number of each part.

In the plunger pump for a waterjet chamber, a pump cam lever, which has been used as a common part, is eliminated, and the power from a pump cam 9 is directly transmitted to the reciprocating mechanism of a piston 3, while smooth movement between the piston and cylinder 2 is secured. Concretely, the piston of the reciprocating mechanism, which moves parallel along the cylinder's axial center is directly actuated by the pump cam via a cam floor 8.