PURPOSE: To restore a destroyed file as against power cut while data is outputted to the file.

CONSTITUTION: A magnetic disk controller with file restoration function 1 is provided with an output control means 2 outputting data to a magnetic disk 7, an output data storage means 3 which stores output data from a host device 9 and which can hold data when power is cut, an output control information storage means 4 which can hold the information on an output position and output data length, which are noticed from the host device 9 and which the output control means 2 records even if power is cut, and an output state storage means 5 which can hold the recording of the state of an output processing which the output control means 2 records even if power is cut and a file restoration means 6 which checks the output state storage means 5 at the time of re-raising and requests re-output to the output control means 2 when power cut during output is recognized.