To provide a book cover that is adaptable to various sizes of books and is quickly and easily attachable to a book.

The book cover 1 comprises: a rectangular cover 3 corresponding to an area of a front cover of a book having a prescribed size; a first surplus part 4 folded back beyond the vertical length of the front cover; and a second surplus part 5 in which both ends including the first surplus part 4 are folded back beyond the lateral length of the front cover. The book cover has: a folding guide line L provided at a position, corresponding to the vertical length of a book having a standard size, in the first surplus part 4; and locking bodies provided so as to lock both sides of the second surplus part 5 and both sides of the rectangular cover 3 located at the rear side of the second surplus part 5 respectively. The first surplus part 4 is folded according to the folding guide line L, thereby forming a book cover corresponding to the book size. The locking bodies allow a user to firmly fix a book.