To provide a fuel injection quantity controller for a diesel engine, which prevents the generation of black smoke by preventing the overshoot of the control rack that has been caused when the engine speed is suddenly raised by full-throttling.

When the driver fully steps on the accelerator pedal to suddenly raise the number of revolutions of the engine running, if the distance between the target rack position and the full rack position is longer than that between the full rack position and the second rack position, the control rack is not moved at a stroke to the full rack position but stopped once at the first rack position for a predetermined period.