In a base station, after CRC is added to transmission data as a detection code, the transmission data is subjected to error-correcting coding using a convolutional code based on tail biting, divided into four frames of P-BCH and transmitted. For this reason, at a mobile station, even if reception (synthesis) is started from any frame of P-BCH represented as (b-1) to (b-4), a cyclic structure of the transmission signal is maintained due to the tail biting and reception data shifted by unit of frame can be obtained. For this reason, at the mobile station, even if a leading frame is unknown, decoding can be executed by one-time error-correcting decoding. A result of the decoding is subjected to CRC detection in four frame timings, the leading frame is detected and the transmission data is restored.