To solve the problem that an existing book jacket, which individually covers each book, makes it difficult to read a plurality of related books while comparing them with one another, because the books have to be read while being compared with one another in the state of being individually opened, when the books are read while being compared with one another.

The books subjected to bookbinding are fixed to the book jackets which are arranged on at least two upper and lower sections while being integrated with one another, respectively. This enables the books in the at least two upper and lower sections to be easily read while being compared with one another, and enables related pages to be concurrently read with ease when the related pages are opened. Additionally, the book jackets are folded in such a manner that the upper book section is superposed on the second book section or later. Thus, even if the books are carried in the folded state of the book jackets when they are shifted to another location, the related pages can be easily opened after the books are carried. In other words, the book jacket can also serve as a bookmark.