To provide a method for reducing the load on a certain sub-network management system when it exceeds an expected amount in a hierarchical distributed type network management system.

A network management object regarding a specified route is simultaneously shifted to a shift destination sub-network management system 21A from a shift originating sub-network management system 21B, the attribute for representing a structural element held by an object related to the route specified by a host sub-network management system 11 is replaced to the shift destination object from the shift originating object, and the destination of an event transfer regarding the route specified by a lower-order sub-network management system or a network element management system 31A is replaces to the shift destination sub-network management system 21B from the shift originating sub-network management system 21A.