PURPOSE: To eliminate the discrepancy of the number and the contents of data on a display device and an a magnetic disk caused by adding, deleting and updating the data by plural programs and to decrease the use resources of a storage device and the magnetic disk, etc., by reading the data on the magnetic disk at the time point when a display request has been received.

CONSTITUTION: When data for displaying the previous page is contained in processing section data 1, a reading-in part 3 reads in data 5 until a value contained in key data 2 is read in, and sends it to an editing part 4. When data for displaying the next page is contained in the processing section data 1, the reading-in part 3 reads and skips data up to the data contained in the key data 2, and sends its succeeding data to the editing part 4. The editing part 4 aligns the data sent from the reading-in part 3 with a format for displaying the data, and at the time point when the data has been aligned with its format, read-in is suspended and displayed. In such a way, the data on a magnetic disk 6 and the data on a display device 7 always coincide with each other.