A rotary machine abnormality detection device for detecting abnormality of a rotary machine having at least first and second rotating bodies (81-1, 81-2), which are configured to rotate axially with respect to a corresponding prescribed axis (813-1, 813-2) while being engaged with each other by having a prescribed space under a normal condition, the device comprising: a vibration measuring portion for, when in use with the rotary machine having at least first and second rotating bodies, measuring a vibration caused by at least one of the first and second rotating bodies (81-1, 81-2); a spectrum processing portion for obtaining a frequency spectrum of measurement data measured by the vibration measuring portion; a feature amount processing portion (222, 222a to 222e) for obtaining a specific feature amount corresponding to a specific frequency component based on the frequency spectrum obtained by the spectrum processing portion; and an abnormality determination portion for determining the existence of abnormality in the rotary machine based on the feature amount obtained by the feature amount processing portion (222, 222a to 222e), characterized in that the feature amount processing portion (222, 222a to 222e) is configured to obtain, from the frequency spectrum, a fundamental wave component F1 of the fundamental wave lobe mesh frequency f1 and n-th harmonic wave components Fn of the n-th harmonic wave lobe mesh frequencies fn up to the least common multiple XAB-th harmonic wave, with n=2 to XAB, wherein a first number of teeth and a first rotational frequency of the first rotating body are represented by MA and VA, respectively, a second number of teeth of the second rotating body is represented by MB, the least common multiple of the first number of teeth MA and the second number of teeth MB is represented by XAB, a fundamental wave lobe mesh frequency obtained by dividing the first rotational frequency VA by the first number of teeth MA is represented by fl, and n-th harmonic wave lobe mesh frequencies with respect to the fundamental wave lobe mesh frequency f1 are represented by fn, with n being an integer ≥ 2, the feature amount processing portion (222, 222a to 222e) is further configured to obtain the specific feature amount based on the obtained fundamental wave component F1 and n-th harmonic wave components Fn. a vibration measuring portion for, when in use with the rotary machine having at least first and second rotating bodies, measuring a vibration caused by at least one of the first and second rotating bodies (81-1, 81-2); a spectrum processing portion for obtaining a frequency spectrum of measurement data measured by the vibration measuring portion; a feature amount processing portion (222, 222a to 222e) for obtaining a specific feature amount corresponding to a specific frequency component based on the frequency spectrum obtained by the spectrum processing portion; and an abnormality determination portion for determining the existence of abnormality in the rotary machine based on the feature amount obtained by the feature amount processing portion (222, 222a to 222e), characterized in that the feature amount processing portion (222, 222a to 222e) is configured to obtain, from the frequency spectrum, a fundamental wave component F1 of the fundamental wave lobe mesh frequency f1 and n-th harmonic wave components Fn of the n-th harmonic wave lobe mesh frequencies fn up to the least common multiple XAB-th harmonic wave, with n=2 to XAB, wherein a first number of teeth and a first rotational frequency of the first rotating body are represented by MA and VA, respectively, a second number of teeth of the second rotating body is represented by MB, the least common multiple of the first number of teeth MA and the second number of teeth MB is represented by XAB, a fundamental wave lobe mesh frequency obtained by dividing the first rotational frequency VA by the first number of teeth MA is represented by fl, and n-th harmonic wave lobe mesh frequencies with respect to the fundamental wave lobe mesh frequency f1 are represented by fn, with n being an integer ≥ 2, the feature amount processing portion (222, 222a to 222e) is further configured to obtain the specific feature amount based on the obtained fundamental wave component F1 and n-th harmonic wave components Fn.