Injector for fuel injection unit

An injector body (B1) is provided with a longitudinal hole (31) eccentrically to the injector body (B1) to install an actuator (3) and a hydraulic power transmission unit (4). A high-pressure fuel passage (1) is disposed in a thick wall portion formed at a side of the longitudinal hole (31). A space in the longitudinal hole (31) functions as a low-pressure fuel chamber (22) and connected to an outer leakage passage. A groove (32) is formed on an inner side wall of the hole 31 to be connected to a low-pressure fuel passage (23) to provide a low-pressure fuel passage groove (26) to discharge leakage fuel from an injection nozzle portion (103) and a control valve portion (102). It is easy to machine the groove (32) integral with the longitudinal hole (31) and to secure strength of a periphery of the high-pressure fuel passage (1).