To provide a bookshelf of both an erected type and an inclined type, for easily switching the erected type and the inclined type, without fear of damaging books to be placed.

This bookshelf has at least two side plates having a plurality of side plate locking parts longitudinally arranged in two rows in the vertical direction of mutually opposite surfaces, at least one shelf board having shelf board locking parts arranged in a position corresponding to the side plate locking parts of the longitudinal two rows, in the vicinity of left-right end parts, and a locking member for detachably joining or engaging with the side plate locking parts, and installing the shelf board in a prescribed position of the side plates by engaging or joining with the shelf board locking parts. The bookshelf of the erected type and the inclined type is characterized by formula: X≥(d/w) × L, wherein a horizontal directional distance between the side plate locking part of a front row and the side plate locking part of a rear row is (w), a pitch between the plurality of side plate locking parts is (d), the vertical directional length of an object to be placed on the shelf board is L, and the length between the rear end part of the depth of the shelf board and the rear end part of the book shelf when the shelf board is provided on the side plates in the horizontal state is X.