PURPOSE: To obtain the secure distribution of corrugated cardboard cases to be conveyed and distributed in each sort by attaching detecting seals on the surface of the corrugated cardboad cases at different passing positions in a conveyer for detecting by an approaching switch.

CONSTITUTION: Thin metal-sheet-shaped detecting seals are attached on the surface of corrugated cardboard cases 1 to be conveyed and distributed in each sort at different passing positions in a conveyer 2 to convey the cases 1, and an approaching switch 4 is provided at the distributing position of cases 1 on this conveyer 2 for detecting the approach and the passage of the detecting seals at passing positions. This construction permits to detect and distribute cases 1 correctly.