An object of the present invention is to perform data clustering while preventing the processing speed from decreasing while maintaining accuracy. A block division section 3 divides a block received from a DB access section 2 into sufficiently small blocks. A block storage section 8 stores blocks supplied from the block division section 3 and hierarchical relationship between the blocks. A block integration section 5 integrates blocks and groups in the order from a hierarchically deeper position to a shallower position based on the stored hierarchical relationship.