A data processing apparatus (100) includes: a temporary storage unit (5) that stores a cluster-element correspondence table showing correspondence between a cluster ID for identifying each of a plurality of clusters classified by the data processing apparatus and an element ID of element data belonging to the cluster identified by the cluster ID, and a group-cluster correspondence table showing correspondence between a group ID for identifying a group classified according to a user's subjective criterion and a cluster ID of a cluster belonging to the group identified by the group ID; a feature extraction unit (1) that extracts a feature value of newly added element data; an automatic classification processing unit (2) that determines a belonging cluster from the plurality of clusters, and updates a classification boundary condition defining a boundary of the belonging cluster according to a predetermined constraint; and a data management unit (6) that records an element ID of the newly added element data and a cluster ID of the belonging cluster, in the cluster-element correspondence table in correspondence with each other.