An air flow amount passing through a centrifugal compressor is acquired on the basis of outputs of an air flow meter. A surge limit compressor rotation speed is acquired on the basis of the obtained air flow amount passing through the compressor. A current compressor rotation speed (turbo rotation speed) is acquired by a turbo rotation speed sensor. A rotation speed of the compressor is controlled on the basis of the surge limit compressor rotation speed and the current compressor rotation speed. More specifically, while being limited so as to be equal or less than the surge limit compressor rotation speed, a target compressor rotation speed is controlled so as to be a value according to the operating conditions, such as accelerator opening and engine speed, of an internal combustion engine. In addition, the surge of the compressor is judged on the basis of the surge limit compressor rotation speed and the current compressor rotation speed.