Abnormal sound detection system

The purpose of the present invention is to detect, among abnormal noises emitted from a device, abnormal noises in which changes in amplitude intensity (sound pressure) do not occur or are negligible, and abnormal noises in which a phase change occurs. This abnormal noise detection system, which diagnoses abnormalities in a device being diagnosed using sound data extracted from the device as an input signal, comprises: a zero point magnitude calculation unit that calculates zero point magnitudes of the sound data for one cycle of the input signal; a zero point density distribution calculation unit that calculates a zero point density distribution from the zero point magnitudes; and a normal/abnormal diagnosis unit that determines whether the device being diagnosed is normal or abnormal by comparing the zero point density distribution of the input signal with the zero point density distribution of normal sound data.