At start of an engine, a fuel injection amount is set to a jump-over injection amount if the engine speed obtained in each cycle is higher than or equal to a determination threshold value, which is set lower than a lower limit of a resonance speed range of powertrain by a predetermined reference value. If the engine speed is lower than the value, the fuel injection amount is set to a step-over injection amount that is smaller than the jump-over injection amount. This setting makes it possible to increase the engine speed such that the engine speed approaches the lower limit of the resonance speed range causing resonance in the powertrain, up to a predetermined range, and then causes the engine speed to jump straight to an engine speed which exceeds the resonance speed range, while in the process of increasing the engine speed by executing the combustion cycles.