A rack includes: a casing; M pairs of supports that are provided inside the casing so as to extend in a depth direction and arrayed at regular intervals in a predetermined direction; and a lock mechanism. The rack can house all returnable containers of one or more prespecified sizes along the respective pairs of supports. The M pairs of supports are arrayed in N rows in an orthogonal direction orthogonal to the predetermined direction. The lock mechanism is configured such that moving first and second shafts that are provided for the respective rows and for the respective tiers, respectively, so as to be movable in the predetermined direction can switch between engagement and disengagement between branches of the first and second shafts and first and second holes, respectively, of the returnable containers.