A first anomaly detection unit detects anomalous first monitored data from among a plurality of first monitored data obtained from a monitored system. A second anomaly detection unit operates in parallel with the first anomaly detection unit and detects anomalous second monitored data from among a plurality of second monitored data obtained from the monitored system. In a first storage unit, the anomalous first monitored data and the anomalous second monitored data detected before lapse of a given time from detection time of the anomalous first monitored data are stored in association with each other. A first determination unit, when the anomalous first monitored data is detected, retrieves the anomalous second monitored data associated with the detected anomalous first monitored data from the first storage unit and outputs a first anomaly detection result including the retrieved anomalous second monitored data and the detected anomalous first monitored data.