To provide an excess energy recovery system for a main engine for consistently maintaining optimum air supply pressure and air supply balance for the operating condition of the main engine without giving adverse effects to the performance of the main engine, even when mounted on part of superchargers for the main engine mounted with the plurality of superchargers.

A generator 7 is connected to the supercharger 5a as part of the plurality of superchargers 5a-5c installed on the main engine 1, and turbine variable nozzles 22b, 22c are provided in the remaining superchargers 5b, 5c, respectively. Air supply controllers 24a-24c compute the rotating speeds of the superchargers from the revolving speed of the main engine 1 and a fuel consumption amount to produce optimum air supply pressure for the main engine. In order that the rotating speed computed by the air supply controllers correspond to rotating speeds detected by rotating speed detectors 23a-23c installed on the superchargers, the air supply controller 24a for the supercharger 5a outputs an output power increasing/reducing signal to a frequency converter 8 and the air supply controllers 24b, 24c for the superchargers 5b, 5c output signals for adjusting nozzle openings to adjust the rotating speeds of the plurality of superchargers 5a-5c.