To provide an abnormality diagnosis device capable of accurately diagnosing even a static appliance, such as a transformer, with a relatively simple configuration.

The abnormality diagnosis device calculates an average and variance for each frequency for frequencies that are an even multiple, odd multiple, or integer multiple of a commercial frequency at not more than 2 kHz or 3 kHz from data in a frequency region of sound sampled for a plurality of times and determines and stores an equipment sound threshold 26. By using the equipment sound threshold 26, upper and lower limits are determined (step 1008), and an unusual sound is diagnosed according to the ratio of the number of abnormal data in the diagnosis period (step 1014). Excess in background noise (BGN) is determined by a threshold 24 of BGN determined similarly for a frequency of not less than 2 kHz or 3 kHz (step 1004), and determination of upper and lower limits (step 1008) and accumulation of data (step 1010) are not performed in the case of excess in BGN.