A power generation system and method including a first heat exchanger, a first thermal engine, and a first power generator on a first working medium line L1 that circulates a first working medium W1, a second heat exchanger, a third working medium supply device that supplies a third working medium W3, and a mixing device for mixing a second working medium W2 and the third working medium. A second thermal engine, and a second power generator are included on a second working medium line L2 that circulates the second working medium. On both of a downstream side of the first thermal engine on the first working medium line and a downstream side of the second thermal engine on the second working medium line, a third heat exchanger is included. Also included is a third working medium discharge device for discharging the third working medium to the third heat exchanger.