A folding box for packing made from a
high density foam
polypropylene resin board, in which the strength in a connecting portion is secured, durability is improved, and
reusability is secured in addition to returnability and recyclability is provided. A folding box for packing is made of
high density foam
polypropylene resin and contains a developed flat box forming board having two box forming bodies (P1) and (P2) respectively including a main face wall (2) extendedly provided on one lateral side thereof with a connecting piece (1), a side face wall (3), and extendedly provided bottom forming boards (4) and cover forming boards (5). A side edge of the bottom forming board (4) of the sub face wall (3) of the box forming bodies (P1) and (P2) is made to be an inclined edge (6) having a 45 degrees angle in respect with a
border line between the sub face wall (3) and the bottom forming board (4), and the inclined edge (6) is extendedly provided with a folding connecting piece (9) having a line for bending into the shape of V (8) for erasing an effect of elastic memory of the
high density foam
polypropylene resin occurring in folding. Respective border lines of respective components of the box forming bodies (P1) and (P2) are made to be lines for bending into the shape of mountain (7) for erasing an effect of elastic memory of the high density foam polypropylene resin. A back surface of the folding connecting piece (9) extendedly provided to the bottom forming board (4) of the sub face wall (3) and a front surface of the bottom forming board (4) of the main face wall (2) opposing to the back surface are connected by heat and pressure-fusion.