To provide a printer which can turn over a page optimally to a booklet bound with a cover sheet and an inner page sheet of mutually differing rigidity.

In this booklet printer, a page turning-over roller featuring the changing of hardness by cooling/warming, can have its frictional force changed by changing the hardness of the roller with the help of a cooling/warming means. Thus, the problem "sheet rigidity difference" can be solved by obtaining the printer to turn over the page with the best-suited roller hardness to the inner page sheet and the cover sheet with mutually differing rigidity.