Data synchronization detection is provided between data identification and code demodulation in a data reproduction system, which performs data synchronization detection using code-modulated data. A specified bit pattern generated in a data codeword is calculated in each phase (bit), using a specified bit sequence pattern that is not generated in a specified phase of the data codeword. For example, a specified bit sequence pattern is generated only in a specified phase of the codeword. The positions of the data codeword partitions are thereby identified. Scrambling is then applied to the write data as required in order to ensure accurate synchronization detection.