To provide a gas turbine capable of realizing high thermal efficiency without surging even when two working fluids are used.

This gas turbine GT is provided with a compressor C for compressing the air, a combustor F for combusting the air compressed by the compressor C with fuel, a turbine T rotated by using a gas of high temperature and high pressure produced in the combustor F, a transmission shaft 1 for transmitting the rotation of the turbine T to the compressor C, a gear part G mounted on the transmission shaft 1 for adjusting a speed of rotation per unit time, to be transmitted to the compressor C, an exhaust gas boiler K producing the steam by using the heat energy of a turbine T outlet, and a supply passage 10 for supplying the steam to the combustor F.