A period is defined to execute the sequences (processes) of communication data acquisition, measuring communication quality, communication quality data acquisition, and channel change. Processing is controlled to execute each process within a time limit set for each process and execute all processes in one cycle. This avoids that a delayed sequence influences and delays other sequences and can suppress delays. If processing fails to finish a sequence, it will resume the same sequence in the next cycle. For communication stations sharing timeslots, there are provided offset periods differing in length before the start of carrier sense in the timeslots for these stations. Consequently, even under a condition in which packet collision may occur, the collision of packets can be avoided by detecting a packet sent to another station by carrier sense. Moreover, by controlling sending priority of packets in the send queue of the gateway, sending delay can be avoided.