To attain better utility of a band capacity utilized for signal transfer.

The method for increasing the utilization of the band capacity includes steps where this invention provides one or more input bit streams each having a transmission rate not in excess of a 1st transmission rate, one or more input bit streams each having a lower band than a 1st band capacity are divided into sub streams, a group belonging to the sub stream and having combined band slightly lower than the 1st band capacity is selected from the sub streams, the selected group of the sub streams is transmitted through a transmission channel and the selected group of the sub stream is combined with output bit streams.