Escalator operation sounds are collected by a remote sound-collecting device 15 or fixed sound-collecting devices 17 and 18, and stored in a data collecting device 21 of a diagnosis device 20. A processing device 22 extracts only abnormal sound components of the escalator operation sound by calculation of a difference between reference data and the sound data stored in the data collecting device 21. The processing device 22 determines an occurrence of an anomaly based on whether a maximum peak P of the abnormal sound components is higher than a predetermined threshold value Sh1. When determined that the anomaly has occurred, the processing device 22 investigates a correlation between a frequency analysis result on data around the maximum peak of the abnormal sound components and abnormal sound frequency patterns pre-stored by causes of anomalies, and estimates the cause of the anomaly based on the investigation.