A controller for an internal combustion engine with a supercharger upstream of an electronically controlled throttle, comprising: a first arithmetic unit that is configured to calculate a target throttle opening degree (TAt) to be given to the electronically controlled throttle 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 that expresses a dynamic relation that is established among the supercharging pressure, a throttle opening degree and an intake air quantity; a second arithmetic unit that is configured to calculate a reference throttle opening degree (TAr) based on the target intake air quantity and a measured value or an estimated value of an atmospheric pressure to be substituted as a throttle upstream pressure, by using a relational expression established between the intake air quantity and an intake pipe pressure in a steady state, and a relational expression that is established among the atmospheric pressure substituted as the throttle upstream pressure, the intake pipe pressure and a throttle flow rate in a steady state, and a monitoring device that is configured to confirm appropriateness of the target throttle opening degree (TAt) that is calculated by the first arithmetic unit with the reference throttle opening degree (TAr) calculated by the second arithmetic unit as a reference, wherein the monitoring device is configured to set a value that is smaller than the reference throttle opening degree (TAr) by a predetermined value as a lower limit value of an appropriate range, to set a value that is larger than the reference throttle opening degree (TAr) by a predetermined value as an upper limit value of the appropriate range and, if the target throttle opening degree (TAt) is included in the appropriate range that is fixed by the lower limit value and the upper limit value, to determine that the value of the target throttle opening degree (TAt) is appropriate. a first arithmetic unit that is configured to calculate a target throttle opening degree (TAt) to be given to the electronically controlled throttle 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 that expresses a dynamic relation that is established among the supercharging pressure, a throttle opening degree and an intake air quantity; a second arithmetic unit that is configured to calculate a reference throttle opening degree (TAr) based on the target intake air quantity and a measured value or an estimated value of an atmospheric pressure to be substituted as a throttle upstream pressure, by using a relational expression established between the intake air quantity and an intake pipe pressure in a steady state, and a relational expression that is established among the atmospheric pressure substituted as the throttle upstream pressure, the intake pipe pressure and a throttle flow rate in a steady state, and a monitoring device that is configured to confirm appropriateness of the target throttle opening degree (TAt) that is calculated by the first arithmetic unit with the reference throttle opening degree (TAr) calculated by the second arithmetic unit as a reference, wherein the monitoring device is configured to set a value that is smaller than the reference throttle opening degree (TAr) by a predetermined value as a lower limit value of an appropriate range, to set a value that is larger than the reference throttle opening degree (TAr) by a predetermined value as an upper limit value of the appropriate range and, if the target throttle opening degree (TAt) is included in the appropriate range that is fixed by the lower limit value and the upper limit value, to determine that the value of the target throttle opening degree (TAt) is appropriate.