To prevent page disorder, page omission and failure of device by detecting insertion of a product in a pocket of a sorter.

In an optical path, the gaps are provided between a fixed light source 3 and a first lens 8, between a second lens 9 and a third lens 10 and between fourth lens 11 and a fixed light detector 4. In the case no product 17 exists, the optical path is formed and the light from the fixed light source 3 passes annularly through a first optical fiber 6 and a second optical fiber 7 and returns to the fixed light detector 4. In the case of no sensing of light, it means that the gap between the corresponding lenses 9 and 10 at the top of the pocket opening is shielded, which indicates whether a product is properly put in or not with an optical sensor 18.