To provide a book opening sustainer which has a function to prevent an opened book page from being turned up by itself, and enables the easy turn-over of the page by a reader.

The book opening sustainer has a spine surface supporting plate body which supports either the upper edge or the lower edge of a face cover, a spine cover and a back cover of an opened book at three sides. In addition, the spine surface supporting plate body has right and left page turn-over prevention parts which hang over in the almost perpendicular direction with respect to the spine surface supporting plate.