To enable conveyance both large-sized articles and small sized articled with one conveying device, and to enable higher conveyance treatment capacity of the small-sized articles than the conveyance treatment capacity of the large-sized articles.

A product conveying device 20 in a conveying system 10 of carton containing products has a main rear conveying body 22, a main front conveying body 24, a sub rear conveying body 26, and a sub front conveying body 28 as two pairs of front and rear conveying bodies movable in the conveying direction in a predetermined basic interval along the conveying direction. When conveying the large sized products 6, the distance between the main rear conveying body 22 and the main front conveying body 24 is expanded to insert the product 6 in the clearance. When conveying the small sized products 7, one small sized product 7 is disposed between the main rear conveying body 22 and the main front conveying body 24, and another one small sized product 7 is disposed between the sub rear conveying body and the sub front conveying body 28.