An automatic payment system includes: first and second conveyer stages arranged along a conveying route on which products are moved; a slope disposed between the first and second conveyer stages on the conveying route; at least one first ID sensor facing the first conveyer stage to sense IDs attached to the products when the products overlap the first conveyer stage; at least one second ID sensor facing the second conveyer stage to sense IDs attached to the products when the products overlap the second conveyer stage; and a bottom ID sensor facing the conveyer route under the slope.