To provide a book cover that is large in a function for protecting an index tag attached to a book, lightly dressed and handy.

This book cover is composed of a hard sheet in which a front surface cover part, a back surface cover part and a rear surface cover part are arranged in series, and which is rectangular in a plane view. A length a from a free end of the front surface cover part to the back surface cover part is equal to a length a from a free end of the rear surface cover part to the back surface cover part. The front surface cover part has an inner pocket for a front cover for holding the book by being inserted with the front surface of the book, and the front surface cover part has a hang-out part which extends by a length b from the inner pocket for the front surface toward the free end of the front surface cover part.