Abstract: A fuel pump has a cam shaft for actuating a pump element to deliver fuel under pressure to an engine. One end of the cam shaft protrudes outside of a pump housing, to which a coupling block is fixedly secured. At least two axially extending threaded holes are formed on the coupling block, and also at least two axially extending through holes are formed on a driving gear for engaging a ring gear of the engine. A head-less locking bolt is screwed into one of threaded holes until the front end thereof abut on the pump housing so that the coupling block is held at a proper position. Thereafter, the driving gear is mounted to the coupling block so that the rear end of the head-less bolt is inserted into one of the through holes and at the same time the driving gear engages with the ring gear of the engine in order to couple the fuel pump to the engine with a synchronous relationship.