A fuel injection device is so constructed that fuel fed from a pressure storage chamber to a valve housing (11) with a nozzle (14) is led to a needle valve back pressure chamber (16) through a groove (21) provided on the peripheral surface of a needle valve (17); a fuel pressure in the back pressure chamber (16) is controlled by opening and closing a pressure regulating port (13) provided in the valve housing by a pilot valve (38) so as to move the needle valve, whereby the nozzle is opened and closed. The pressure regulating port is opened and closed by a drive control of the pilot valve with a valve drive unit by means of elongation and contraction of the magnetostrictive rods attributable by the action of an external magnetic field. The magnetostrictive rods, consisting of first and second magnetostrictive rods (34 and 35), are axially arranged side by side in parallel to the pilot valve.