PROBLEM TO BE SOLVED: To provide an abnormality detection system for a gas turbine which ensures safe driving even during abnormal time.SOLUTION: An abnormality detection system includes: a state quantity acquisition part to acquire a state quantity of a plant and machinery; an abnormality determination part that compares the state quantity with a predetermined threshold value, and determines that the plant and machinery are in an abnormal state when the state quantity exceeds the threshold value for a predetermined period of time; and a command value output part to output a target load for the plant and machinery in a previously set abnormal time.SELECTED DRAWING: Figure 1