Control section 125 at base station 100 in a CDMA/TDD mobile communication system assigns one or more fixed forward link time slots to a plurality of time slots divided at a communication frame at a predetermined interval, and forward link time slots and reverse link time slots to the time slots except for the fixed forward link time slots by allocating corresponding to a ratio of a total information volume of a forward link to a total information volume of a reverse link in the system, in order to transmit a control channel signal including a synchronization control channel signal using the fixed forward link time slots, and to transmit forward link and reverse link traffic channel signals using the forward link time slots and the reverse link time slots that are allocated according to the number of time slots respectively required corresponding to the respective information volume.