Packets are transmitted from an apparatus to another apparatus via a plurality of carrier waves. The apparatus calculates, for each of the plurality of carrier waves, a tolerance parameter indicating a tolerable margin of the current line-quality value for causing a change of a modulation method to be used, based on a line-quality value received from the another apparatus, and allocates packets to the plurality of carrier waves based on a service-quality level assigned to each of the packets and the tolerance parameter calculated for each of the plurality of carrier waves, such that a first packet having the service-quality level equal to or higher than a second packet is allocated, on a priority basis, to a first carrier wave having the tolerance parameter equal to or larger than a second carrier wave to which the second packet is allocated.