A sign of a minor rubbing abnormality of a slide bearing in a diesel engine is accurately detected. In order to realize the accurate detection, the following is performed: detecting waveform data which represents an acceleration of a vibration which occurs when a slide bearing is in operation; transforming acceleration waveform data into an acceleration spectrum of a frequency domain by applying a Fourier transform to the acceleration waveform data; quantifying a plurality of peak information which occurs at a rotational frequency interval of a shaft to be measured in the acceleration spectrum by performing a predetermined signal process combined with rotational frequency information of the shaft; obtaining a characteristic value; monitoring whether the obtained characteristic value has exceeded a predetermined threshold value; and when the characteristic value has exceeded the threshold value, determining that an abnormality has occurred in the slide bearing.