Fluctuation detection device and fluctuation detection method

A fluctuation detection device (1) is provided with: a deviation characteristic quantity calculation unit (31) that calculates a deviation characteristic quantity by performing frequency analysis on a deviation between a value of operation instruction information (SP) input to an operator (10) that drives an operation end of a feedback control system and a value of behavior information input to the operator (10); the behavior information is either an output (MV) from an operator (10) to an operation end or a control amount of a control object; a similarity feature amount calculation unit (32) that performs frequency analysis on the values of the operation instruction information (SP) and the behavior information, and calculates similarity feature amounts of the operation instruction information (SP) and the behavior information; and a fluctuation determination unit (4) that determines, on the basis of the deviation feature amount and the similarity feature amount, whether or not there is a fluctuation phenome