An engine body includes a plurality of cylinders, and the intake valve lift-amount of each cylinder is changed based on the engine operating state. A pressure sensor continuously detects the intake pressure, which is the pressure in an intake pipe, to detect the intake pressure decrease amount, which is the amount of decrease in the intake pressure caused due to execution of the intake stroke, of each cylinder. The air quantity variation correction coefficient, which is used to compensate for the variation in the in-cylinder supplied-air quality with each cylinder, is calculated based on the detected intake pressure decrease amount, and the fuel injection amount is corrected using the air quantity variation correction coefficient.