Control apparatus for internal combustion engine

An ECU (50) calculates an intake air amount based on output of a boost pressure sensor (48) that is very responsive and has good intake air amount calculating accuracy, when an advance amount (±) of a valve closing timing of an exhaust valve (36) is within an advance reference value (¸1). Also, if the advance amount (±) becomes greater than the advance reference value (¸1) due to valve timing control, it is determined that there is error in the output of the boost pressure sensor (48) due to blowback of exhaust gas, so the intake air amount is calculated based on the output of an airflow sensor (24). Thus, the method used to calculate the intake air amount can be appropriately selected as the situation demands based on the advance amount (±) of the exhaust valve (36) (i.e., the exhaust gas blowback amount), so various controls that use the intake air amount can be accurately executed.