To provide a transitional load control device for keeping the power output of a gas turbine in a selected output level.

A transitional control device to a gas turbine control device cooperates with a suspended type speed governor to generate a fuel instruction for regulating the fuel flow rate to the combustor of a gas turbine. A proportion + integration control device provided in the transitional control device determines a power output set point when switching stage is started, and this set value is compared with the present power output of the gas turbine. An output signal showing the difference between the present power output and the set point generated by the proportion + integration control device is applied to the suspended type speed governor to compensate the fluctuation of the power output of the gas turbine during transitional stage.