An intake air base amount calculation unit respectively calculates a base air amount Gbase, an intake air temperature correction coefficient Ka and a pulsation correction coefficient Kb, and calculates an intake air base amount Gnb based on these. An internal EGR amount calculation unit calculates an clearance volume EGR amount based on an exhaust valve closing timing EVC, and further calculates a backflow EGR amount based on a valve overlap amount OL, a rotation speed of engine Ne and an intake pipe pressure Pm, and still further calculates an internal EGR amount Gegr by adding the clearance volume EGR amount and the backflow EGR amount. Then, an intake air amount calculation unit calculates an intake air amount of cylinder Gn by subtracting the internal EGR amount Gegr from the intake air base amount Gnb.