PURPOSE: To increase an extension exchange range and also to improve the effective use of a radio time slot by controlling this time slot for each repeating frequency.

CONSTITUTION: An extension exchange system consists of a switchboard 1, a base station 2, repeater stations 3, 30 and 40, and slave stations 4, 5 and 50. In a communication system, the radio time slots are allocated between the station 2 and the satellite stations 3-5 and 30-50 respectively. Then the communication circuits are switched at the same station 3 when the communication is carried out between the station 2 and the calling and called sides 6 and 7 via the same station 3. In such a constitution, the communication route is minimized in the system and the radio time slots of the higher order stations 2, 40 and 50 which are occupied by the station 3 can be opened to the communication carried out among the stations of other frequency levels.