Abstract: A multistage supercharging system for a reciprocating engine, which is suitable for use in an aircraft capable of flying at high altitude, includes plural stage turbochargers connected in series to each other. A control unit controls operation of these turbochargers. The turbocharger at each stage includes a turbine side bypass passage bypassing the turbine, a compressor side bypass passage bypassing the compressor, a wastegate valve for controlling the flow rate of exhaust flowing through the turbine side bypass passage, a bleed valve for controlling the flow rate of intake air flowing through the compressor side bypass passage, and a pressure sensor disposed at the downstream side of the compressor. The control unit receives a signal from the pressure sensor, and controls the respective valves to selectively operate the turbochargers.