The optical disk player is capable of correctly restarting to write data. Data protection means returns an optical pick-up from an interruption address to a synchronization starting address. The data protection means reads data from the synchronization starting address to the interruption address at a reading velocity equal to a former writing velocity. The data protection means restarts writing data from the interruption address if a phase of data read is synchronized with a phase of data to be written. The data protection means returns the optical pick-up to the synchronization starting address and reads data from there to the interruption address at a reading velocity slower than the former writing velocity so as to synchronize the phases if the synchronization is failed.