Abstract: Turbines (21b, 31b) and compressors (21a, 31a), which constitute superchargers (21, 31), are disposed in series on an exhaust gas passage (3) and an air intake passage (2), respectively. The supercharger (31) is equipped with a supercharger rotation sensor (61), which transmits a detection signal obtained according to the rotation of the compressor (31a) to a control device, a bypass passage (4), which bypasses exhaust gas from the upstream side to the downstream side of the turbine (31b), and a bypass valve (34), which regulates the flow rate of exhaust gas flowing through the bypass passage (4). Control device (60) regulates the rotational speed of the compressors (21a, 31a) in a high-efficiency range by producing a control signal based on the detection signal from the supercharger rotation sensor (61), and sending the control signal to the bypass valve (34).