An ECU preliminarily obtains a target supercharging pressure determined based on an engine rotational speed and an engine load, and stores the target supercharging pressure value. The ECU commands a flow passage area changing unit to set an exhaust gas flow passage area to the maximum flow passage area or the minimum flow passage area, and judges the abnormality of a supercharger by comparing supercharging pressure detected by a supercharging pressure sensor and the stored target supercharging pressure.