A fuel supply system for an internal combustion engine capable of executing calculation of an energization time of the electromagnetic valve at proper timing and thereby properly controlling the amount of fuel to be discharged from the fuel pump toward a fuel injection valve. In the fuel supply system, when a predetermined timing corresponding to a predetermined crank angle position of the engine deviates from a predetermined cam angle timing which is within a predetermined time period including a timing at which a top of a cam nose of the driving cam is abutting a plunger, and preceding and following the timing, and corresponds to a predetermined rotational angle position of the driving cam, the calculation timing of the energization time is corrected such that the calculation timing is made closer to the cam angle timing.