Turbines and compressors, which constitute superchargers, are disposed in series on an exhaust gas passage and an air intake passage, respectively. The supercharger is equipped with a supercharger rotation sensor, which transmits a detection signal obtained according to the rotation of the compressor to a control device, a bypass passage, which bypasses exhaust gas from the upstream side to the downstream side of the turbine, and a bypass valve, which regulates the flow rate of exhaust gas flowing through the bypass passage. Control device regulates the rotational speed of the compressors in a high-efficiency range by producing a control signal based on the detection signal from the supercharger rotation sensor, and sending the control signal to the bypass valve.