PURPOSE: To carry out favorable radio communication even when an interior transmission line of a radio section is used, by appropriately dividing a necessary time slot for service of the radio section and transmitting each divided time slot by means of one radio carrier pair.

CONSTITUTION: When subscribers of a certain number or more are to be accommodated, the number of radio frequencies is increased. When all time slots carried by the subscribers accommodated to a certain radio frequency are used, the remaining subscriber terminals are changed to another radio frequency, at which vacant time slots exist, by means of the frequency changing instruction of a host station so that they can make communication. When such arrangement is made, all terminals can use all time slots on all radio carriers and the same traffic as that of a system having the same time slots at one frequency can be processed. Moreover, since the receiving frequency band becomes narrower, the receiving sensitivity can be improved.