A management node for managing a program update time refers to an update management table in which a plurality of managed nodes are classified into a plurality of groups and the sequence of program updating of the groups is defined. The management node sequentially selects the groups in accordance with the sequence of program updating in such a manner that after program updating processing has been completed in all managed nodes included in the selected group, the next group is selected. The management node refers to the update management table, transmits a program update request to each of the managed nodes included in the selected group, receives an update completion notification from the managed node, and notifies update management information storing means that the update processing has been completed in the managed node.