In a magnetic disk processing apparatus, read command processing instructs reading data out to compare a physical address (PA) of data which has been read out with a PA being retained. If the addresses coincide with each other, then processing returns to a command executing operation and, if not, after a flag condition is ascertained by a flag determining operation, a seek command is issued for a PA being stored independently of the software. A flag indicates that a seek command, resulting from a mismatch of a comparison, has been completed and the processing returns to read command processing. In this manner, any seek error caused by a mismatch of seek address management which occurs between a seek command from software and a patrol seek is compensated for.