A detected data processing apparatus includes a selecting unit that calculates mutual correlation between a plurality of groups of detected data acquired from a detecting unit that detects an operational state of a circuit board, and then selects as analysis data the detected data of a group whose value indicating correlation with other groups is smaller than a threshold value set up in advance; and a first calculating unit that calculates a first Mahalanobis distance on a basis of a first Mahalanobis space generated by using the analysis data selected by the selecting unit from the detected data obtained when a normal circuit board is operated and on a basis of the detected data obtained when a circuit board of diagnosis target is operated.