An engine (100) provided with a variable series supercharging system (7) composed of a high-pressure supercharger (10) and a low-pressure supercharger (20), a supercharging pressure sensor (63) for detecting the pressure of intake air pressurized by the variable series supercharging system (7), a high-pressure supercharger rotation sensor (61) for detecting the rotational speed of the high-pressure supercharger (10), a variable actuator (14) for adjusting the capacity of the high-pressure supercharger (10), and a control device (60) capable of controlling the variable actuator (14). The control device (60) controls the variable actuator (14) based on detection signals from the supercharging pressure sensor (63) and the high-pressure supercharger rotation sensor (61).