A foldable case blank having first, second, third and fourth portions continuously connected through longitudinal fold lines, these portions being formed as upper, bottom, front and rear portions of a case, respectively, when the blank is fabricated as a case and side pieces attached through transverse fold lines of these first through fourth portions on both side ends thereof. The first, i.e. upper, portion is provided with shaping portions which are defined by longitudinal cut lines, transverse foldable lines and a central cut line so that the shaping portions reinforce the side portions of a fabricated case when the shaping portions are folded inwardly of the case. The shaping portions are provided with projections along the central cut line so that the projections are engaged with engaging holes formed on the bottom portion of the case when the case blank is fabricated. The upper portion is further provided with tongued pieces which are engageable with the engaging holes of the bottom portion when one case, thus fabricated, is stacked on another fabricated case.