PURPOSE: To carry out more precise quantity adjustment to an injection device in which additional fuel is fed into a chamber just before a valve seat in a nozzle needle valve under an excessive pressure before the discharge of an injection valve is initiated by connecting an additional fuel conduit to a return conduit through a controllable closing valve.

CONSTITUTION: Fuel fed from a working chamber 3 in an injection pump constituting member 11 reaches a chamber 14 in an injection nozzle 11 by way of a hole 9 of a nozzle holder 10, and is injected from a jet hole when a nozzle needle 13 is pushed up overcoming a spring force. In this arrangement, a transfer pump 16 supplies additional fuel from an additional fuel tank 15 into the camber 14 through a pressure chamber 17, a passage 22 in the nozzle holder 10 and a check valve 23. The passage 22 can be connected thereto with a return conduit 26 through the intermediary of a control valve 24. Further, the control valve 24 is controlled by a control unit 25, and accordingly, when the control valve 24 is closed, kinetic energy of the additional fuel is converted into potential energy so as to produce impulsive pressure.