1. A load decentralization method for decentralizing load centralized to a MAP of a hierarchical domain in a network where packets destined to mobile nodes in the network are transmitted to the mobile nodes via the MAP, the MAP including a table part for managing a corresponding relation of home addresses and Care-of-Addresses of the mobile nodes in the hierarchical domain, the method comprising the steps of: providing a same function as the MAP to at least a portion of routers situated in the hierarchical domain of the MAP; moving one of the elements in the table part to the portion of the routers when a congestion of the MAP is detected; and actuating the portion of the routers to operate as a substitute of the MAP.