A relay device in a communication network includes: a configuration determination unit determining whether a configuration frame is received; a comparison unit; first and second configuration units; and a configuration transfer unit. The comparison unit determines whether the propagation number at reception time is equal to the total number of target devices in a configuration frame. When the propagation number is not equal to the total number, the first configuration unit sets a port in the transfer destination information to the mirror output port. When the propagation number is not equal to the total number, the configuration transfer unit outputs the updated configuration frame from the mirror input port. When the propagation number is equal to the total number, the second configuration unit sets a port in the transfer destination information to the mirror output port.