To enhance a page turning-over precision regardless of a change in the number of booklet pages between a booklet pressing member and a turning-over roller, depending upon the number of pages to be turned over, although the change actually occurs.

When a booklet 2 is pressed into contact with the turning-over roller 10 by means of the booklet pressing member 13 pushed forward to an advance position D, and under this state, the turning-over roller 10 is rotated as steps of a page bulging process, the advance position D of the booklet pressing member 13 is corrected in accordance with information on the pages of the booklet 2 to be turned over. Thus a pressure contact force which presses the booklet 2 into contact with the turning-over roller 10 by the booklet pressing member 13 can be optimized, regardless of a change in the number of pages 2a between the booklet pressing member 13 and the turning-over roller 10. Consequently, the page turning-over precision can be enhanced.