An IP address is assigned to each of IP bearers, and a mobile anchor device (GWN) 33, which serves as an anchor in a mobile communication system, manages association among an identifier of a mobile terminal 7, those IP addresses, and identifiers that identify radio access means. A handover between different radio access networks 1 and 3 is implemented by assigning an IP address already used in a handover source IP bearer to a handover destination IP bearer. Accordingly, it is possible to provide a mobile communication system and a communication method for enabling a handover between radio transmission paths respectively established by different radio communication methods in a next generation mobile communication system.