The invention relates to a control device of an internal combustion engine capable of suppression of fuel efficiency deterioration caused by unnecessary long duration of the supercharging pressure reserve control at switching of the combustion. In the internal combustion engine (10) provided with a turbocharger (22), a throttle valve (24), and a WGV (42), if there is a request for switching from stoichiometric combustion to lean combustion and also there is a request for raising a supercharging pressure after the switching of combustion to a pressure higher than the supercharging pressure before the switching of combustion, the supercharging pressure reserve control for raising the supercharging pressure while a requested intake air amount (S) required for realizing a requested torque of the internal combustion engine (10) in the stoichiometric combustion is maintained is executed by using the throttle valve (24) and the WGV (42). After the supercharging pressure reserve control is finished, the switching of combustion is executed. When an actual supercharging pressure reaches the lower of a requested supercharging pressure (L) and a realizable supercharging pressure, the supercharging pressure reserve control is finished.