the unique word at the timing set by the aperture control module 2 and determines the success failure in detection of the unique word and the phase of the unique word based on the correlation value and the correlation threshold set by the correlation threshold setting module 7 and outputs the determination results as the unique word detection information the timing control module 3 aperture control module 2 and aperture width setting module 6 constitute the receive timing control means that outputs timing information for controlling the receive timing of the unique word detector module 1 the timing control module 3 controls the receive timing according to the unique word detection information the frame synchronization determining module 5 determines the frame synchronization state according to the number of consecutive detections or consecutive miss of the unique word detection information designated by the guard level setting module 4 and outputs the determination results as the frame synchronization information the aperture width setting module 6 outputs the aperture width which is going to be used when the unique word detector module 1 attempts to detect the next unique word based on the unique word detection information and the frame synchronization information the correlation threshold setting module 7 outputs the correlation threshold which is going to be used when the next unique word is detected based on the unique word detection information and the frame synchronization information the frame structure determining module 10 predicts the frame structure based on the detected intervals and phase of the unique words in the unique word detection information the embodiment.