A common rail type fuel injection system of an engine includes: a common rail for accumulating and holding high-pressure fuel; a fuel pump for pressure-feeding fuel to the common rail; and an injector for injecting the high-pressure fuel accumulated and held in the common rail. A pressure sensor is disposed in a fuel suction port of the injector. An ECU sequentially detects a fuel pressure varied when the injector injects the fuel and sequentially detects a fuel pressure varied when the fuel pump pressure-feeds the fuel. When the injector injects the fuel, the ECU computes injection pressure by the detection values of these pressures and computes injection characteristics by the injector on the basis of the injection pressure.