PURPOSE: To detect the side displacement of a load on a pallet by providing vertically opposed photoelectric sensors on the center of a horizontal roller making contact with the side surface of the pallet and a horizontal beam rotated integrally with the roller, respectively.

CONSTITUTION: When a pallet 2 is carried on a roller conveyor 3 in the state where a load 1 inclined around the vertical axis is placed thereon, and reaches between detecting devices 4, 4, right and left horizontal rollers 9, 9 make contact with the side surfaces of the pallet 2 to rotate rotating frames 8, 8 forward. Since a part of the load 1 is protruded to the side of the pallet 2, then, a lower sensor 10 on the side where the load 1 is protruded is shielded by the load 1 to detect this protruding. The side protruding quantity of the load 1 to the pallet 2 detectable by the lower photoelectric sensor 10 is determined depending on the diameter of the horizontal roller 9. Since performed with the pallet as a standard, this detection has no error even if the pallet 2 is inclined.