Disclosed is an injector for fuel injection systems of internal combustion engines, especially direct injection diesel engines. Said injector comprises a piezo actuator (16) that is disposed in an injector body (10) and rests against the injector (10) and a sleeve-type transmission piston (32) via first spring means (34). The inventive injector further comprises a nozzle body (20) which is connected to the injector body (10) and is provided with at least one nozzle outlet (26, 27) and in which a staggered valve needle (21) is guided in an axially movable manner, and second spring means (48) that are arranged inside the transmission piston (32) and maintain the valve needle (21) in the closed position along with the injection pressure that affects the rear end of the valve needle (21). The injector also comprises a control space (42) that is embodied at the end of the transmission piston (32), which faces the valve needle, and is connected to a fuel supply (18) via a leak gap (43, 45, 47), said fuel supply (18) being subjected to injection pressure. The valve needle (21) is impinged upon in the opening direction (35) by the fuel located in the control space (42). An essential characteristic of the invention consists of the fact that the transmission piston (32) actuated by the piezo actuator (16) is spatially directly allocated to the valve needle (21) such that a rearward area (30) of the valve needle (21), which has a larger diameter than an area of the valve needle (21) located at the nozzle outlet end, fits into the interior (31) of the transmission piston (32).