To provide a storage box with a knockdown shelf being easily assembled and having an excellent durability when disposing a heavy load and in earthquakes.

In this storage box 1, one-side surface of each side plate 4 has the width shorter than that of the side plate 4 by the thickness of a back plate 5, shelf plate support means that are projectingly provided with a plurality of crosspieces 7b supporting the side edges of shelf plates 6 at equal intervals and bases (a) extending in the longitudinal direction are previously fixed thereto, and the upper edges and the lower edges of the bases 7a are press-fitted in and temporarily fixed to horizontal slits 8 provided near respective side edges at the base of a top board 2 and the upper face of the basal plate 3. This storage box is further provided with L-cross-sectional corner stays 11 with flanges 11A that extend longitudinally along the respective corners of the box 1 for hiding joints between the side plates 4 and the back plate 5 and the shelf plate support means 7 and are press-fitted in slits 9 and 10 that are longitudinally formed on the back plate 5 and the shelf plate 6, a top face restriction cover 12 and a base restriction cover 13.