<p>A booklet provided with multiple leaves (2), a spine (4) that joins the bound edges of the leaves (2) with a flexible glue layer (3), and a front cover (5) and a back cover (6), of which the entire surface portions at least are respectively continuous with the entire surface portion of the spine (4). The flexural strength of the spine (4) backed by the glue layer (3) is set so that the spine (4) can bend inward at an acute angle along with the bound edges of the leaves (2) when the center pages of the leaves (2) are opened.</p>