A pressure accumulation type fuel injection system for accumulating high-pressure fuel, which is pressurized and pressure-fed by a fuel supply pump driven by an engine, in a common rail and for injecting the high-pressure fuel accumulated in the common rail into a cylinder of the engine through an injector, the pressure accumulation type fuel injection system including a pressure safety valve that opens when the fuel pressure in the common rail exceeds a limit set pressure in order to limit the fuel pressure in the common rail to the limit set pressure or under, comprising: fuel pressure sensing means for sensing the fuel pressure in the common rail; and an engine control unit for controlling the engine to avoid further continuation of an abnormally high-pressure state, in which the fuel pressure in the common rail sensed by the fuel pressure sensing means exceeds at least one of a pump usage allowable area, the fuel pressure in the common rail above which adversely affects reliability of the fuel supply pump, and an injector usage allowable area, the fuel pressure in the common rail above which adversely affects reliability of the injector, when the abnormally high-pressure state continues for a predetermined period; wherein the engine control unit includes abnormality diagnosing means for detecting an abnormality failure of the injector when an abnormally high-pressure state, in which the fuel pressure in the common rail sensed by the fuel pressure sensing means exceeds a determination value corresponding to the injector usage allowable area, continues for a predetermined period; and the engine control unit demands limitation of an engine output of the engine or an idle-up operation for increasing idling rotation speed of the engine when the abnormality failure of the injector is detected by the abnormality diagnosing means, wherein the engine control unit includes rotation speed sensing means for sensing engine rotation speed; characterized in that the determination value corresponding to the injector usage allowable area is calculated in accordance with the engine rotation speed sensed by the rotation speed sensing means. fuel pressure sensing means for sensing the fuel pressure in the common rail; and an engine control unit for controlling the engine to avoid further continuation of an abnormally high-pressure state, in which the fuel pressure in the common rail sensed by the fuel pressure sensing means exceeds at least one of a pump usage allowable area, the fuel pressure in the common rail above which adversely affects reliability of the fuel supply pump, and an injector usage allowable area, the fuel pressure in the common rail above which adversely affects reliability of the injector, when the abnormally high-pressure state continues for a predetermined period; wherein the engine control unit includes abnormality diagnosing means for detecting an abnormality failure of the injector when an abnormally high-pressure state, in which the fuel pressure in the common rail sensed by the fuel pressure sensing means exceeds a determination value corresponding to the injector usage allowable area, continues for a predetermined period; and the engine control unit demands limitation of an engine output of the engine or an idle-up operation for increasing idling rotation speed of the engine when the abnormality failure of the injector is detected by the abnormality diagnosing means, wherein the engine control unit includes rotation speed sensing means for sensing engine rotation speed; characterized in that the determination value corresponding to the injector usage allowable area is calculated in accordance with the engine rotation speed sensed by the rotation speed sensing means.