A diesel engine has a fuel injection nozzle to which pressurized fuel is supplied from a pump. The nozzle has a pressure sensor detecting the fuel pressure and a lift sensor sensing a lift magnitude of a needle valve. An electronic control unit (ECU) computes a variation ratio of the fuel pressure value which is measured by the pressure sensor. The ECU computes a non-increasing point in an increasing part of variation ratio and judges the point to be a timing for starting the fuel injection of the nozzle. The EPU also computes the actual fuel injection amount in accordance with the fuel injection timing as well as the fuel pressure and the lift amount of the needle valve both at the various points. The EPU controls the actual injection amount to be identical to a target fuel injection amount.