A control device for an internal combustion engine comprising: a supercharger provided at an exhaust side in the internal combustion engine and supercharging intake air by use of energy of exhaust gas; an exhaust system capacity change unit configured to change an exhaust system capacity which is a sum of a capacity of an exhaust manifold and a capacity of a space communicating with the exhaust manifold of the internal combustion engine; an exhaust purification device provided at a downstream side of the supercharger, and purifying the exhaust gas of the internal combustion engine; an exhaust gas recirculation path communicating the exhaust side at an upstream side of the supercharger with the intake side and flowing a part of the exhaust gas to the intake path; a valve opening control unit configured to control an opening degree of a throttle valve provided in an intake path of the internal combustion engine; and an air-fuel ratio control unit configured to control an air-fuel ratio depending on a driving state of the internal combustion engine, wherein the valve opening control unit adjusts the opening degree of the throttle valve, such that the opening degree of the throttle valve is increased, depending on a reduction in an intake air amount due to a reduction in supercharging efficiency of the supercharger caused by increasing the exhaust system capacity, when the air-fuel ratio control unit makes the air-fuel ratio rich and the exhaust system capacity change unit increases the exhaust system capacity, during a regeneration process of the exhaust gas purification device, wherein the exhaust system capacity change unit is an isolation valve provided near an exhaust gas inlet of the exhaust gas recirculation path. a supercharger provided at an exhaust side in the internal combustion engine and supercharging intake air by use of energy of exhaust gas; an exhaust system capacity change unit configured to change an exhaust system capacity which is a sum of a capacity of an exhaust manifold and a capacity of a space communicating with the exhaust manifold of the internal combustion engine; an exhaust purification device provided at a downstream side of the supercharger, and purifying the exhaust gas of the internal combustion engine; an exhaust gas recirculation path communicating the exhaust side at an upstream side of the supercharger with the intake side and flowing a part of the exhaust gas to the intake path; a valve opening control unit configured to control an opening degree of a throttle valve provided in an intake path of the internal combustion engine; and an air-fuel ratio control unit configured to control an air-fuel ratio depending on a driving state of the internal combustion engine, wherein the valve opening control unit adjusts the opening degree of the throttle valve, such that the opening degree of the throttle valve is increased, depending on a reduction in an intake air amount due to a reduction in supercharging efficiency of the supercharger caused by increasing the exhaust system capacity, when the air-fuel ratio control unit makes the air-fuel ratio rich and the exhaust system capacity change unit increases the exhaust system capacity, during a regeneration process of the exhaust gas purification device, wherein the exhaust system capacity change unit is an isolation valve provided near an exhaust gas inlet of the exhaust gas recirculation path.