A control device is provided capable of reliably preventing occurrence of a surging state by judging a possibility of the surging state in a relatively easy manner and promptly executing a surging state avoidance control. When a supercharging pressure decreasing state in which a target supercharging pressure decreases is detected, an operating speed of a wastegate valve is determined based on a detected engine rotational speed. That is, by lowering the operating speed as the engine rotational speed lowers, reduction in flow rate of the air passing through a compressor is prevented, and the occurrence of the surging state is reliably prevented. By lowering the operating speed instead of changing a target opening degree of the wastegate valve, a maximum opening degree of the wastegate valve can be suppressed, and responsiveness in the case where an acceleration request is made immediately after deceleration of an engine can be improved.