A certifying system for checking validity of a radio tag passing through a predetermined route includes a route information writing section that writes information relating to a route passed by the radio tag on the radio tag, a route information acquisition section that acquires information relating to the route written on the radio tag by the route information writing section, a storage section that stores information relating to a regular route preset corresponding to the ID of the radio tag, and a certifying section that checks the validity based on the information relating to the route written on the radio tag acquired by the route information acquisition section and the information relating to the regular route stored in the storage section.