A desired wastegate valve opening degree is set in accordance with a driving condition of an internal combustion engine; based on a detected rotation speed of the internal combustion engine and a set desired wastegate valve opening degree. An ECU determines whether or not supercharging air to the internal combustion engine is required. If the supercharging air is not required and if the opening degree of the wastegate valve becomes a desired valve, a driving current supplied to the wastegate actuator from a wastegate valve driving unit is stopped.