The packing box (10) is provided with: a bottom wall (12); end walls (13A, 13B) that stand on first edges of the bottom wall (12); side walls (15A, 15B) that stand adjacent to the end walls (13A, 13B); edge walls (20) that are connected to the side edges of the end walls (13A, 13B) via outer wall folding lines (21); foldback walls (25) that are disposed on the inner surfaces of the edge walls (20); inner walls (27) that are disposed on the inner surfaces of the end walls (13A, 13B); and reinforcing walls (26) that are continuous with the foldback walls (25) via first folding lines (29) and are continuous with the inner walls (27) via second folding lines (30). The reinforcing walls (26) protrude toward the inside from between the foldback walls (25) and the inner walls (27). Of the first and second folding lines (29, 30), the first or second folding lines (29, 30) that are located on the outer wall folding line (21)-side of the apex of the protrusion are disposed at a distance (L3) from the outer wall folding lines (21).