A fuel injection apparatus for internal combustion engines, in which the onset and end of injection are determined by a hydraulically actuated control slide. The injection pump of the apparatus, which is preferably combined with an injection nozzle to form a pump/nozzle unit, has a pump piston embodied as a differential piston, whose section having the larger diameter serves as an auxiliary pump piston and generates a control pressure (p.sub.S) actuating the control slide. During its compression stroke the control slide, in order to initiate the onset of injection, closes an overflow line leading out of the pump work chamber; and during its return stroke, which is effected by the pressure drop in the control line, the control slide relieves the overflow line in order to control the end of injection. The control pressure (p.sub.S) in the control line necessary for actuating the stroke movement of the control slide is controlled by the closure of this line by means of a control device and is built up during the compression stroke of the auxiliary pump piston.