Abstract: A shelf engagement mechanism includes supports, taper sleeves, shelves, and rings. A plurality of annular engagement grooves are formed on a surface of each support and are arranged at predetermined longitudinal intervals. Each taper sleeve has a projection formed on an inner surface thereof and is attached to the support such that the projection is fitted into one of the annular engagement grooves. Each taper sleeve is tapered such that a diameter of an outer profile increases from a first end toward a second end. A ring is provided at each of four corners of the shelf. The ring is tapered such that a diameter of an inner profile increases from the first end toward the second end so as to be coincident, partially or entirely, with the outer profile of the taper sleeve. The ring is fitted onto the taper sleeve, which, in turn, is fitted onto the support.