A fuel-flow-rate control device, a power generation system, and a fuel-flow-rate control method which can prevent overshooting of a gas turbine output (gas turbine inlet temperature) and which can improve power generation efficiency are provided. The fuel-flow-rate control device includes a computing portion for obtaining a state quantity relating to operating conditions and temperature conditions of a gas turbine as an input signal and computing a fuel-flow-rate command for controlling a fuel flow rate supplied to a combustor based on the above input signal, and a second selection circuit for setting the above fuel-flow-rate command to be not more than a fuel-flow-rate upper limit. The fuel-flow-rate upper limit is a fuel flow rate at which the gas turbine inlet temperature is set to be not more than a predetermined upper temperature limit.