PURPOSE: To treat the recording unit of a registered identification number as erased at the time of reproduction so as to improve the reliability of the erasing process by registering the identification number of the recording unit which has become an object to be erased in a specific management area on a recording medium when the data erasing operation on the recording medium fails.

CONSTITUTION: Delivery and reception of recording and reproduced data 3 are performed between the host device 1 of a re-writable type magneto-optical disk device and a recording and reproduction controller 2 and the controller 2 makes a completion report 5 against a READ/WRITE instruction 4. Moreover, an access controller 9 controls an optical head 12 in accordance with the instruction 10 of the controller 2 and a magnetic head driver 14 set the magnetizing direction of a magnetic head 13 prior to the recording and erasing operations of the head 13 in accordance with WRITE magnetizing direction designation 15 are erasure magnetizing direction designation 16. Then a laser power controlling section 17, out-of-track detection circuit 27, selector ID discrimination circuit 34, etc., treat the recording unit of an identification number registered in a specific area of a recording medium as erased at the time of reproduction.