Abstract: The method is disclosed for checking the accuracy of folding a parallelepiped box made from a cardboard blank (1) comprising four adjacent panels (Pa, Pb, Pc, Pd), at least some edges of the panels being associated with flaps (Ra1, Ra2, Rb1, Rb2, Rc1, Rc2, Rd1, Rd2) for closing the top and bottom surfaces of the box. Slots (5, 6) with parallel edges are formed between the adjacent flaps. In the method, the spacing between the edges of the slots (5, 6), produced between the flaps (Ra1, Rd1 Ra2, Rd2) when the outer panels are folded together, is compared with a predetermined standard spacing between the edges of the slots (5, 6) to determine whether the folded box is defective.