An acquisition unit is configured to acquire measurement values of a target device. The measurement values that are acquired include at least a temperature and a flow rate of an input fluid to be input to the target device, and a temperature and a flow rate of an output fluid to be output from the target device. A correction unit is configured to obtain a correction measurement value by which the measurement values are corrected through thermal equilibrium calculations based on the measurement values. A distance calculation unit is configured to calculate a Mahalanobis distance with a factor of the correction measurement value.