Inter-cluster data transfer system and data transfer method

In a hierarchical multiprocessor system in which a plurality of clusters, each of which is a multiprocessor wherein a plurality of processors share a memory, each of data collecting units 31 of master processors 10-1 and 20-1 in clusters 10 and 20, respectively, collects at regular. time intervals data to be transferred from its own cluster to the other cluster; transferable data generating units 32 generates combined transferable data by putting together the remaining data after the removal of duplicates from the collected data; transferable data transfer units 33 transfers the generated combined transferable data to the master processor in the destination cluster; transferable data receiving units 34 receives combined transferable data transferred from the master processor in another cluster; and transferable data distributing units 35 distributes the received combined transferable data to processors in its own cluster.