PURPOSE: To prevent an overshoot when a rated speed is reached and to prevent speed variations when a cntrol motor is switched.

CONSTITUTION: An acceleration control system compares the acceleration setting being output from an analog switch 21 with the differentiated value of a turbine speed by a differentiator 23 and outputs the proportional-plus-integral value to a transfer gate. A speed/load control system matches a speed setting value CFN and actual speed NHP, and the proportional calculation value by a gain setting 15 is output to the transfer gate. Prior to the transfer to a speed/load control mode, a value proportional to the speed deviation is selected by the analog switch 21 as the setting value for the acceleration control system. As the speed is increased, the acceleration setting is decreased, and when the rated speed is reached, the acceleration setting becomes zero, then the speed/load control is selected by the transfer gate. A hold circuit 18 is provided on the speed/load control system to prevent speed variations during the switching.