PURPOSE: To judge anomaly speedily and correctly by outputting a trip signal by judging the variation rate of the revolution speed detection signal of a high- pressure shaft, in a gas turbine equipped with a high-pressure shaft system and a low-pressure shaft system.

CONSTITUTION: A low-pressure shaft system 25 for driving a generator 7 and a high-pressure shaft system 26 equipped with a combustor 2 are provided. A high-pressure shaft speed detector 38 is arranged oppositely to a gear 37 for speed pick-up which is arranged onto a high-pressure shaft 3a. The signal supplied from the detector 38 is input into a misfire detecting protector 35, and the misfire state is judged from the variation rate of the detection signal. When the misfire state is judged, a gas turbine trip signal (k) is outputted into a trip apparatus 21. Therefore, the anomaly of the gas turbine can be judged rapidly and correctly.