Abstract: An anomaly detection system includes: a register value collector that collects register values of register numbers from a controller; a future state predictor that predicts a future state of the control system; a blacklist creator that creates a blacklist based on a prediction result; an anomaly determiner that determines whether the control system enters an anomalous state by checking the collected register values against the blacklist; and an outputter that outputs a determination result. The blacklist creator defines, as the blacklist: a predicted register number that is predicted, if a register value of the predicted register number is changed, to cause the control system to enter the anomalous state in the future; and a range of the register value within which the control system is predicted to enter the anomalous state, and dynamically creates the blacklist corresponding to a combination of the collected register values.