An object of the present invention is to enable monitoring whether a target throttle opening degree to be given to an electronically controlled throttle is not out of an appropriate range, in a controller for an internal combustion engine with a supercharger. To this end, in a controller according to the present invention, propriety of the target throttle opening degree is confirmed with a reference throttle opening degree as a reference by a monitoring device. The target throttle opening degree is calculated based on a target intake air quantity and a measured value or an estimated value of a supercharging pressure by using an inverse model of an air model expressing a dynamic relation that is established among the supercharging pressure, a throttle opening degree and an intake air quantity, by a first arithmetic unit. The reference throttle opening degree is calculated based on the target intake air quantity and a measured value or an estimated value of an atmospheric pressure by using a relational expression that is established between the intake air quantity and an intake pipe pressure in a steady state, and a relational expression that is established among a throttle upstream pressure, the intake pipe pressure and a throttle flow rate in a steady state, by a second arithmetic unit.