A control device for an internal combustion engine with a turbocharger, the control device comprising: an exhaust bypass path that is installed in an exhaust system for the internal combustion engine to bypass the turbocharger; a WGV that is installed in the exhaust bypass path and capable of arbitrarily adjusting the opening thereof upon receipt of an operation request from the internal combustion engine; acquisition means for acquiring, during a transient operation of the internal combustion engine, an exhaust gas flow rate of exhaust gas discharged from the internal combustion engine, a WGV opening, and a boost pressure correlation value having a correlation with boost pressure of the internal combustion engine as a transient exhaust gas flow rate, a transient WGV opening, and a transient boost pressure correlation value, respectively; virtual exhaust gas flow rate acquisition means for acquiring, as a virtual exhaust gas flow rate, a virtual value indicative of the exhaust gas flow rate prevailing when the transient boost pressure correlation value and the transient WGV opening are achieved during a steady operation of the internal combustion engine; virtual turbine flow rate acquisition means for acquiring, as a virtual turbine flow rate, a virtual value indicative of a flow rate of exhaust gas passing through a turbine for the turbocharger (hereinafter referred to as a turbine flow rate), the virtual value prevailing when the transient boost pressure correlation value and the transient WGV opening are achieved during the steady operation; flow rate ratio acquisition means for acquiring a flow rate ratio of the virtual turbine flow rate to the virtual exhaust gas flow rate; and turbine flow rate calculation means for calculating the turbine flow rate during the transient operation by applying the flow rate ratio to the transient exhaust gas flow rate. an exhaust bypass path that is installed in an exhaust system for the internal combustion engine to bypass the turbocharger; a WGV that is installed in the exhaust bypass path and capable of arbitrarily adjusting the opening thereof upon receipt of an operation request from the internal combustion engine; acquisition means for acquiring, during a transient operation of the internal combustion engine, an exhaust gas flow rate of exhaust gas discharged from the internal combustion engine, a WGV opening, and a boost pressure correlation value having a correlation with boost pressure of the internal combustion engine as a transient exhaust gas flow rate, a transient WGV opening, and a transient boost pressure correlation value, respectively; virtual exhaust gas flow rate acquisition means for acquiring, as a virtual exhaust gas flow rate, a virtual value indicative of the exhaust gas flow rate prevailing when the transient boost pressure correlation value and the transient WGV opening are achieved during a steady operation of the internal combustion engine; virtual turbine flow rate acquisition means for acquiring, as a virtual turbine flow rate, a virtual value indicative of a flow rate of exhaust gas passing through a turbine for the turbocharger (hereinafter referred to as a turbine flow rate), the virtual value prevailing when the transient boost pressure correlation value and the transient WGV opening are achieved during the steady operation; flow rate ratio acquisition means for acquiring a flow rate ratio of the virtual turbine flow rate to the virtual exhaust gas flow rate; and turbine flow rate calculation means for calculating the turbine flow rate during the transient operation by applying the flow rate ratio to the transient exhaust gas flow rate.