PURPOSE: To reach a desired output safely and speedily by varying the value of a control gain regarding a control element which is fast in response according to whether the deviation is large or small.

CONSTITUTION: A torque control means 2 compares measured torque with a torque set value to find its deviation e2 similarly to a turbine exit temperature limiting means 1. When the obtained deviation e2 exceeds the specific value a2, a control gain KθA which is large enough to secure the stability of a control system is selected and outputted to a low-order selecting means 3, but when the obtained deviation e2 does not exceed the specific value 8a2, on the other hand, a control gain KθB which is small enough to cause no overshooting is selected and outputted to the low-order selecting means 3. Thus, when a limitation gain regarding the control element which is fast in response is selected, a limiter is not selected to make the value large while the deviation e2 is large, and when the deviation e2 decreases below the specific value e2, the limiter is selected to make the value small.