A clustering processing apparatus comprises: N clustering units that group samples included in the data block into clusters, each clustering unit sequentially taking each sample as a target, grouping the target sample into one of the clusters within the data block, storing cluster information including identification on each cluster into which the samples are grouped within the data block, and storing sample assignment information indicating the cluster to which the target sample belongs; a cluster information transferring unit that selects cluster information on a cluster to be integrated from the cluster information when a predetermined condition is met, and transfers the selected cluster information to a third storage unit; and an updating unit that integrates clusters selected based on the cluster information stored in the third storage unit into an integrated cluster, and updates the sample assignment information based on information of the integrated clusters.