A processor determines, when a frame is received, whether a total of current learning numbers stored in a second storage unit has reached a total of maximum learning numbers. The processor identifies in the second storage unit, if it is determined that the total of current learning numbers has reached the total of maximum learning numbers, a first group identifier associated with a lower priority than a priority associated with a reception group identifier contained in the frame. The first group identifier is associated with a first current learning number not less than a first minimum learning number associated with the first group identifier. The processor replaces a first correspondence relationship including the first group identifier with a reception correspondence relationship among a port number of a port at which the frame has been received, a source address contained in the frame, and the reception group identifier.