A gas turbine engine optimization control device estimates a specific fuel consumption using a given control parameter of a variable mechanism, determines a change between a specific fuel consumption estimation value by the control parameter of the variable mechanism in a previous operation period and a specific fuel consumption estimation value by the control parameter of the variable mechanism in this operation period, determines a new control parameter of the variable mechanism with which the specific fuel consumption estimation value approaches a minimum, adds the new control parameter of the variable mechanism to a preset control parameter initial value, and sets the addition value to be a control parameter command value of the variable mechanism in a next operation period.