A pressure sensor is located in a fuel passage, which extends from a pressure-accumulation vessel to a nozzle hole of a fuel injection valve. The pressure sensor is located closer to a nozzle hole than the pressure-accumulation vessel for detecting pressure fluctuated by injection of fuel through the nozzle hole. An instruction signal output unit outputs an injection instruction signal so as to instruct an injection mode of fuel to the fuel injection valve. A defective injection determination unit determines whether a detected pressure of the fuel pressure sensor is fluctuated in a fluctuation mode in a range assumed from the injection instruction signal. The defective injection determination unit determines that a defective injection occurs when determining that the detected pressure is out of the fluctuation mode in the assumed range.