1. A clustering processing apparatus that groups data including a plurality of samples into clusters, comprising: N clustering units, configured to group, for corresponding one of N data blocks resulting from dividing the data, samples included in the data block into clusters within the data block, each clustering unit sequentially taking each sample included in the corresponding one of the N data blocks as a target sample, grouping the target sample into one of the clusters within the data block, storing, in a first storage unit, cluster information including identification information on each cluster into which the samples are grouped within the data block, and storing, in a second storage unit, sample assignment information indicating the cluster to which the target sample belongs; a cluster information transferring unit, configured to select, for each of the data blocks, cluster information on a cluster to be integrated from the cluster information stored in the first storage unit when a predetermined condition is met, and transfers the selected cluster information from the first storage unit to a third storage unit; and an updating unit, configured to integrate clusters selected based on the cluster information stored in the third storage unit into an integrated cluster, and updates the sample assignment information stored in the second storage unit based on information of the integrated clusters.