PURPOSE: To enable to simplify adjustment of injection timing and to enable it microscopically, by making a position of a casing adjustable with an adjusting screw device from the outside.

CONSTITUTION: When an error ±α exceeds an allowable range, for example, when necessity to delay injection timing by (l) is come about, a lock nut 53 is slackened and the whole of a casing 41 is displaced to a main body A of a pump by turning an adjusting screw 52 of an adjusting screw device 50. A timer piston 31, therefore, energized elastically to a lid body 43 by a spring 32 is moved also in a tangential direction of a roller ring 11 along with the casing 41, the roller ring 11 is turned and its set position, that is, injection timing is adjusted so that it comes to an A point. Accordingly the casing 41 is locked on that adjusting position by tightening the lock nut 53 thereafter.