To downsize an oil pump for separation lubrication which adopts no back gear, and uses engine rotation as a driving source even when the engine is rotated in an inverse direction.

A distributor 2 is fitted to a cylinder 1a arranged on the pump main body 1 in a rotatable and axially movable manner. A shaft 2a which is arranged on the opposite side to a pump chamber of the distributor 2 is covered with a worm wheel 4 to be meshed with a driving worm 6. A pin 10 inserted into the shaft 2a is loosely fitted to a recession formed on the worm wheel 4. A lead cam 4a arranged on the worm wheel 4 is in press-contact with a discharging amount setting cam 5 by means of a spring 7 arranged between the distributor 2 and a plunger 3 which is then in press-contact with a lid 9 covering the cylinder. Suction and discharge passages 2b, 2c are formed on the distributor 2 so as to be communicated with a pump chamber and opened to a peripheral surface of the distributor. Discharge ports 1b, 1c and a suction port are formed on the pump main body 1 so as to be agreed with the opening of the suction and discharge passages 2b, 2c in an axial direction of the cylinder.