PURPOSE: To eliminate the need for manual allocation management by adding an identifier generated by a slave set according to a prescribed rule, and allowing a master set to allocate based on request a time slot of a frame relevant to the identifier requested to the master set.

CONSTITUTION: A master set 1 displays a time slot(Ts) number going to be allocated from now to an outgoing frame and awaits the reception of an allocation request signal from slave sets 2-4. Each of the slave sets sends a Ts allocation request signal with an identification number added thereto generated at starting from each of identification number generating circuits 5a, 5b, 5c not overlapped with each other to the master set 1. In this case, each slave set delays a transmission timing of the Ts allocation request signal by a time corresponding to the identification number to avoid collision and contention. The set 1 detects the identification number based on a request of the slave sets and allocates the Ts of the relevant frame. Thus, the excellent point, multi- point transmission not requiring manual complicated Ts allocation management is implemented.