Abstract: A cogeneration system is provided which is capable of reliably switching a bypass damper even if a supply of electric power is shut off in an abnormal state etc. and which is unlikely to leak exhaust gas and is cost-effective even if it is increased in size. To this end, an exhaust gas path (10) for introducing exhaust gas from a gas turbine (2) into an exhaust-heat-recovery heat exchanger (8) is provided with a bypass path (11) and an inlet of the bypass path (11) is provided with a bypass damper (12) which is controlled so as to be opened and closed by an air cylinder driven by compressed air from the compressor (3).