A method is disclosed for optimizing packet transmission paths in a mobile communication network (400) in which packets are transmitted and received between mobile stations (10-14) or between a mobile station and a fixed network (120) by way of a plurality of packet transmission device (60-64, 70-72, 80, and 81) and radio base stations (50-57). When a mobile station uses a service that is provided by a fixed network (300), imposed are applied on the packet transmission path such that packets pass by way of specific packet transmission devices (80 and 81) depending on the fixed network (external network) 300. When the mobile station uses a service that is provided by the mobile communication network (400), on the other hand, no restrictions are imposed on the packet transmission path, and the packet transmission path is thus set such that the link costs are a minimum.