A relay apparatus converts a received multicast frame to a unicast frame, sets a relatively higher communication rate than a specified communication rate, and forwards the converted unicast frame to a communication apparatus at the relatively higher communication rate. The relay apparatus attaches conversion information, which represents execution of the conversion, to the unicast frame. On reception of a unicast frame from the relay apparatus, the communication apparatus determines whether the received unicast frame is the converted unicast frame from the multicast frame, based on the conversion information attached by the relay apparatus. Upon determination that the received unicast frame is the converted unicast frame, the communication apparatus reconverts the received unicast frame to a multicast frame and transfers the reconverted multicast frame to an application installed in the communication apparatus to utilize a multicast frame. This arrangement enables the communication apparatus to effectively utilize a received unicast frame that is a converted unicast frame from a multicast frame.