PURPOSE: To prevent unevenness of printing from occurring in a printing book or the like and to enhance printing quality by directly supporting the opened page of a booklet and uniformizing the printing pressure.

CONSTITUTION: A bearing plate 11 is inserted between the opened page 8(13) of a booklet S and the next page 9 and bears the rear 8b of the opened page 8(13). A pair of bearing plates 11 are provided for one side 12 and the other side 13 of the opened page 8 of the booklet S. A supporting plate 14 is equipped to support the cover Sa of the opened booklet S. The bearing plates 11 are provided turnably and successively to the supporting plate 14. The bearing faces of the bearing plates 11 are formed of an elastic member 17. In the case of printing through a printer, the booklet S is conveyed together with an underlay 10 and information is printed on the surface 8a of the opened page 8(13) of the opened booklet S through a printing head. In the case, even when the booklet S has many pages and is thick, the opened page 8(13) of the booklet S is directly borne by the bearing plate 11. Therefore printing pressure is uniformized in the respective parts and such a state is prevented that printing on the surface 8a to be printed is made thin.