A gas turbine engine comprising: a variable mechanism; a sensor associated with the variable mechanism; and a gas turbine engine optimization control device comprising: a specific fuel consumption estimation operation section configured to estimate a specific fuel consumption using a sensor feedback value of a control parameter of the variable mechanism given for each predetermined operation period; a control parameter reoperation section configured to determine a change between a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in a previous operation period and a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in this operation period, and to determine a new control parameter command value of the variable mechanism with which the specific fuel consumption estimation value (SFC_est) approaches a minimum; and a control parameter command value operation section characterized in that it is configured to add the new control parameter command value of the variable mechanism determined by the control parameter reoperation section to a preset control parameter initial value of the variable mechanism, and to output the value as a control parameter command value of the variable mechanism in a next operation period. a variable mechanism; a sensor associated with the variable mechanism; and a gas turbine engine optimization control device comprising: a specific fuel consumption estimation operation section configured to estimate a specific fuel consumption using a sensor feedback value of a control parameter of the variable mechanism given for each predetermined operation period; a control parameter reoperation section configured to determine a change between a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in a previous operation period and a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in this operation period, and to determine a new control parameter command value of the variable mechanism with which the specific fuel consumption estimation value (SFC_est) approaches a minimum; and a control parameter command value operation section characterized in that it is configured to add the new control parameter command value of the variable mechanism determined by the control parameter reoperation section to a preset control parameter initial value of the variable mechanism, and to output the value as a control parameter command value of the variable mechanism in a next operation period. a specific fuel consumption estimation operation section configured to estimate a specific fuel consumption using a sensor feedback value of a control parameter of the variable mechanism given for each predetermined operation period; a control parameter reoperation section configured to determine a change between a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in a previous operation period and a specific fuel consumption estimation value (SFC_est) based on the sensor feedback value of the control parameter of the variable mechanism in this operation period, and to determine a new control parameter command value of the variable mechanism with which the specific fuel consumption estimation value (SFC_est) approaches a minimum; and a control parameter command value operation section characterized in that it is configured to add the new control parameter command value of the variable mechanism determined by the control parameter reoperation section to a preset control parameter initial value of the variable mechanism, and to output the value as a control parameter command value of the variable mechanism in a next operation period.