The radio relay apparatus 1 stores MAC addresses of the radio terminals 2a and 2b and IP addresses assigned to the radio terminals 2a and 2b by the DHCP server 5 on the IP network 4 in the memory unit of the radio relay apparatus 1. The radio relay apparatus 1 monitors the information of MAC addresses and IP addresses of the source radio terminal and the destination radio terminal included in the packet routed through its own apparatus, and based on the address information stored in the memory unit, when it determines that the radio terminals 2a and 2b communicate each other via its own apparatus, transitions from the first communication mode over the IP network 4 to the second communication mode not over the IP network 4.