PROBLEM TO BE SOLVED: To secure a sufficient time to communicate packet information.SOLUTION: A base station transmits a beacon 16 repeatedly at a transmission period Tp. One time slot is set in a time zone after one beacon is transmitted and before a next beacon 16 is transmitted. On receiving uplink packet information 18 from a terminal device in an uplink time zone US, the base station includes acknowledgement information, destined to a transmission source terminal device of the uplink packet information, in the beacon 16 to be transmitted in the next time slot. The base station extracts a transmission source address from the uplink packet information, to include the transmission source address, as a destination address, in the acknowledgement information. When the terminal device receives the beacon 16, if acknowledgement information destined to the self-device is included in the beacon 16, the terminal device recognizes from the acknowledge information that the uplink packet information is received in th
