PURPOSE: To prevent the collision of an idle/busy signal by sending out a data signal in which a preamble signal is introduced only when no transmission inhibiting signal is incorporated in a read signal.

CONSTITUTION: A communication equipment 25 and plural base stations 1-3 are connected by a transmission line 7, plural base stations 1-3 and plural mobile stations 4, 5 are connected by a bidirectional radio channel, respectively, and communication is executed between the communication equipment 25 and plural mobile stations 4, 5 by the bidirectional radio channel through the base stations 1-3. Also, plural mobile stations 4, 5 are provided with a means for transmissing a transmission requesting signal to the base stations 1-3, respectively, and plural base stations 1-3 transmit a transmission permitting signal until a transmission requesting signal is received, respectively. Moreover, when the transmission requesting signal is received, a transmission inhibiting signal for inhibiting the transmission of other mobile stations 5 (4) than the mobile stations 4 (5) corresponding to this transmission requesting signal is transmitted only during the time allocated to its own station in time zones brought to multiplex time division of plural base stations 1-3, respectively. In such a manner, even if the base stations 1-3 generate different busy/idle signals, the collision of the busy/idle signal can be prevented.