In a data transmitting and receiving method of a demand assignment type, a master device schedules an occupancy band of a fixed size for requesting a band to the master device by slave devices, with respect to a specific number of slave devices for each cycle, and the slave device waits for assignment of the occupancy band of the fixed size based on the schedule and performs message transmission of requesting a band for data transmission to the master device, thereby suppressing an influence of pressure on the data transmission band and preventing line utilization efficiency from decreasing while avoiding signal collision on a Random Channel.