PURPOSE: To judge surely the state of a magnetic disc by providing a discriminating means discriminating whether or not an error occurs during read/write and a counter means counting the number of retrial operations at the occurrence of error based on the result of discrimination of the said discriminating means.

CONSTITUTION: A control circuit 1 decides whether or not an error occurs during read/write by checking a status register of a CPU interface 21 of an FDC2, stores command information to the FDC2, track information, sector information, side information and status information of the FDC2 to a buffer memory 5 when the error occurs, counts the number of retrial operations at that time and stores also this count value to the buffer memory 5. When the number of retrial operations exceeds a predetermined number of times, the information relating to the content of error is read from the buffer memory 5 and a message in response to the content of error is displayed on a CRT display 7.