Abstract: An abnormal irregularity cause display device includes a process data acquisition unit that reads, from a storage device, the pieces of process data, an abnormality determination unit that calculates an abnormality degree representing an extent of an irregularity of process data of the pieces of process data read by the process data acquisition unit, a cause diagnosis unit that determines, for each of the pieces of process data, whether the abnormality degree calculated by the abnormality determination unit satisfies a predetermined criterion by using causal relation information defining a combination between a cause and the irregularity, which appears as an influence resulting from the cause, of the process data output by each of the plurality of sensors, and an output control unit that reads, from the storage device, the information indicating the handling and makes an output device output the information.