A first fuel flow rate command value indicating a command value of a fuel input amount is calculated so that an output of a gas turbine matches a target output. An upper limit value of the first fuel flow rate command value is calculated based on a deviation obtained by subtracting, from an estimated value of a turbine inlet temperature of the gas turbine, a second limit value relating to the estimated value set such that the estimated value does not exceed a first limit value of the turbine inlet temperature.