PURPOSE: To compose in a compact size by holding a main shaft rotatable with a casing, installing an eccentric cam eccentric to the main shaft, and installing a connecting ring rotatable relatively with the eccentric cam.

CONSTITUTION: When a pump main shaft 12 is driven and rotated, an eccentric cam 15 is rotated integrally with the shaft 12, and a connecting ring 20 installed rotatable relatively with the cam 15 carries out a revolutional movement same as the revolutional movement of the axial center C3 of a collar 15 around the axial center C1 of the shaft 12. As a result, pump plungers 22 and 23 linked to the ring 20 are reciprocated inside the cylinder holes of pump cylinders 25. And as a result, by the functions of check valves 28 and 29, the oil is sucked into the chambers of the cylinders 25 when the plungers 22 and 23 are in the expansion stroke, through oil passages 2a and 2b, oil flow holes 3a and 3b, and an oil passage hole 25c, then the oil is released to an oil passage 4 from the cylinder chambers in the contraction stroke through an oil passage hole 25d and an oil flow hole 3c, and the operation is transmitted to the plungers 22 and 23 from the ring 20.