To fix a bulkhead body into which an operation screw rod linked to a piston is screwed and inserted, to an inner wall of a pump cylinder by employing a detent and retainer mechanism of simple structure.

In a height adjusting oil pump wherein the bulkhead body 6 for closing one end of the pump cylinder 2 is penetrated, the operation screwing rod 10 for regulating the height is screwed and inserted along an inside and an outside, the piston 3 disposed on a tip end is advanced and treated in an axial direction in the pump cylinder 2 while operating rotation of the operation screwing rod 10 from the outside, and operating oil for regulating the height is supplied and delivered; the bulkhead body 6 is subjected to noncircular deformed fitting 7 for adapting at least a part of an outer peripheral surface to the pump cylinder 2, detent operation is carried out, and retainer operation is also carried out by putting a lock ring 8 between the bulkhead body 6 and an inner circumferential surface of the pump cylinder 2.