A fuel injection pump for a diesel engine for attaining a specially excellent combustion performance, specifically comprising a notch part (20) formed in the retraction collar (16) of a delivery valve (3), in addition to an Angleich cut(17), to increase the communicating area of a fuel path (18) between a high pressure chamber (7) and a force-feed chamber (11) according to the lift of the delivery valve (3) so as to suppress the retraction effect of the delivery valve (3) in order to prevent a residual pressure in the high pressure chamber (7) from excessively reducing particularly during high idling. An annular groove (54) communicating with a lower lead (52) is formed in the outer peripheral surface of a plunger (50), and a part of fuel inside the force-feed chamber (11) is returned, during force-feed process, to a fuel feed port (13) through the annular groove (54) so as to increase the length of an injection period in low and medium speed ranges to reduce combustion noises, and to delay the injection timing under low idle condition to reduce the emission of blue white smoke.