To provide a drive shaft damage diagnosis device, capable of discriminating both exfoliation and abrasion of a cross of the drive shaft from a raw waveform outputted from a displacement sensor, when diagnosing damage to the drive shaft of a rolling facility or the like.

A processing means, for detecting the damage state of the drive shaft from an output from the displacement sensor, includes a smoothing means for smoothing the output wave from the displacement sensor by moving average, an FFT transformation means for performing FFT transformation of the smoothed output wave from the displacement sensor, an inverse-FFT transformation means for removing the rotational synchronous components from a spectrum, acquired by the FFT transformation and transforming into a time base waveform by inverse-FFT, an abrasion determination means for determining the abrasion state from the mean value of the waveform acquired by the inverse-FFT transformation, and an exfoliation determination means for determining the exfoliation state from the amplitude of the waveform acquired by the inverse-FFT transformation.