An LP table retains a combination of a physical port and a VLAN identifier in association with a logical port. When a frame is received at the physical port, a table processing unit acquires a logical port based on the LP table. An FDB processing unit learns a source MAC address contained in the received frame in association with the logical port acquired by the table processing unit to an FDB. A plurality of logical ports are set for the physical port by the LP table. A loop prevention unit prohibits frame relay between the plurality of logical ports set for the physical port.