The gas turbine system (GT) includes a combustor (2) having a fuel injection nozzle assembly (4) for jetting hydrogen gas (H) and pure water (W), a reservoir (12) for pooling the pure water (W) to be supplied to the combustor (2), a gas compressing device (10) for boosting the hydrogen gas (H) to be supplied to the combustor (2), a fuel supply passage (6) for guiding the boosted hydrogen gas (H) towards the combustor (2), and a pressurizing passage (16) communicating between the reservoir (12) and the fuel supply passage (6) for pressurizing the pure water (W) by means of the boosted hydrogen gas (H).