PURPOSE: To shorten the time of a data compare operation by executing the compare operation of an original or copy data storage part after the data restoring is completed for the block unit of the data storage part when the power source of a doubling file control device is turned on and when the data are restored from a magnetic disk device for saving the data to an original and copy data storage part.

CONSTITUTION: When the power source of a doubling file control device is turned on and the data from a magnetic disk device to original and copy data storage parts 2 and 3 are restored, interruption is applied to the comparing part when the data restoration of the block unit is completed by a magnetic disk control part, and the interruption is applied to the comparing part when the data restoration of the same block unit as the magnetic disk control part is completed by other magnetic disk control part. Thus, the comparing part executes the compare operation of the original and copy data storage parts 2 and 3 of the block unit and this is continued until the data restoration is completed. Thus, the completion of the data compare operation can be completed simultaneously when the data restoration operation is completed.