Abstract: A steam-injection type gas turbine system provided with a waste-heat boiler uses surplus steam effectively for cooling the stationary blades of a turbine. The steam-injection type gas turbine system includes an air compressor (2) for compressing air, a combustor (3) for mixing a fuel with compressed air to burn the fuel, a turbine (4) driven by the energy of a combustion gas produced by the combustor (3), a waste-heat boiler (10) using an exhaust gas (G) discharged from the turbine (4) as a heat source, a steam supply system (23) for distributing steam generated by the waste-heat boiler (10) to the combustor (3), the stationary blades (68B) of the turbine (4) and external steam loads (22), and a steam distribution adjusting means (32) for preferentially supplying steam to the external steam loads (22), adjusting the rate of supply of steam to the combustor (3) and supplying the rest of the steam to the stationary blades (68B).