A rotating machine abnormality detection device for detecting an abnormality of a rotating machine including a rotating body by using a sensor that detects an elastic wave generated from the rotating machine, the rotating machine abnormality detection device comprising: an acquisition unit configured to acquire data generated by using a signal output from the sensor, the data being obtained by arranging an intensity value indicating intensity of the elastic wave on a time-series basis; a first determination unit configured to determine that the rotating machine is abnormal when an intensity ratio exceeds a first threshold as a result of a first process, the first process being defined as a process of sequentially dividing the intensity value contained in the data by a predetermined reference intensity value to calculate the intensity ratio, and sequentially comparing the intensity ratio with the predetermined first threshold to determine whether the intensity ratio exceeds the first threshold; a second determination unit configured to perform a second process every time a predetermined period elapses, the second process being defined as a process of, when the predetermined period has elapsed, calculating an average change rate of the data in the predetermined period to determine whether the average change rate is within a predetermined range; and an update unit configured to update and lower the reference intensity value when it is determined as a result of the second process that the average change rate is within the range, wherein when the reference intensity value is updated, the first determination unit performs the first process by using the updated reference intensity value in the next predetermined period. an acquisition unit configured to acquire data generated by using a signal output from the sensor, the data being obtained by arranging an intensity value indicating intensity of the elastic wave on a time-series basis; a first determination unit configured to determine that the rotating machine is abnormal when an intensity ratio exceeds a first threshold as a result of a first process, the first process being defined as a process of sequentially dividing the intensity value contained in the data by a predetermined reference intensity value to calculate the intensity ratio, and sequentially comparing the intensity ratio with the predetermined first threshold to determine whether the intensity ratio exceeds the first threshold; a second determination unit configured to perform a second process every time a predetermined period elapses, the second process being defined as a process of, when the predetermined period has elapsed, calculating an average change rate of the data in the predetermined period to determine whether the average change rate is within a predetermined range; and an update unit configured to update and lower the reference intensity value when it is determined as a result of the second process that the average change rate is within the range, wherein when the reference intensity value is updated, the first determination unit performs the first process by using the updated reference intensity value in the next predetermined period.