Upon receipt of a synchronization request from the CPU, the AAL1 device of the act system causes its cell forming section to extract the allocation position information for the SAR-PDU payload about a particular time slot in the current frame and, via the synchronization information send/receive section, transfers the information to the AAL1 device of the standby system. The AAL1 device of the standby system causes its operation processing section to calculate the allocation position of a particular time slot in the next frame for the SAR-PDU payload based on the above allocation position information. The AAL1 device of the standby system starts allocation of the data of and following a particular time slot of the next frame to the SAR-PDU payload starting from the position indicated by the calculation result.