To selectively use a temporary address with different upper 64 bits as a transmission source IPv6 address in a situation in which two network prefixes or more can be obtained.

A device 2 receives router advertisements with different network prefixes from routers 3 and 4 and generates temporary addresses including respective network prefixes. The device 2 refers to a network prefix of a transmission source address during present communication and uses a temporary address including a network prefix different from that of the previous network prefix as a transmission source address in the next communication.