A data processing apparatus includes: a temporary storage unit storing a cluster-element correspondence table showing correspondence between a cluster ID for identifying each 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 extracting a feature value of newly added element data; and an automatic classification processing unit determining a belonging cluster from the clusters, and updating a classification boundary condition defining a boundary of the belonging cluster. The apparatus also includes a data management unit recording an element ID of the newly added element data and a cluster ID of the belonging cluster.