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.