To enable a folding storage box easily shaken under its developed state in a box-like shape to be positively held at its box-like shape by improving its structural strength.
This storage box is comprised of a box base segment 1, a developed segment 2 folded and stored against the box base segment 1, a lid member 3 closing an upper surface of the developed segment 2 and a bottom surface wall 4 for closing a bottom surface of the developed segment 2. Under a state in which the upper surface of the developed segment 2 is closed by the lid member 3 under its developed state, a lid circumferential frame 29 of the lid member 3 is engaged with the upper end of the developed segment 2 to enable a box shape of the developed segment 2 to be positively held with the lid 3.