According to a device and a method for controlling an internal combustion engine, a control device (38) enables controllability of the internal combustion engine to be improved by preventing surging from occurring upon starting or stopping of the internal combustion engine, by opening a relief valve (26) as a rotational speed of an exhaust turbine supercharger (12) reaches a surging rotational speed when the control device (38) causes a motor generator (32) to assist in rotation of the exhaust turbine supercharger (12) upon starting of a diesel engine body (11).