A collision detection unit detects whether a first entry that is associated with a value obtained by hashing a first MAC address is present in each area in a MAC address table and detects whether a second entry that is associated with a value obtained by hashing a second MAC address is present in each area in the MAC address table. If the first entry is present in each of the areas, a collision avoidance control unit acquires the second MAC address stored in the first entry that is present in one of the areas and inputs the second MAC address in the collision detection unit. If the second entry is not present in any of the areas in the MAC address table, a registration unit stores the second MAC address in the second entry and stores the first MAC address in the first entry.