To provide a caser wherein the corner surface of a corner cut carton can be formed in an appropriate shape even when the folding line cutting of a flap is weak.

In the caser 10, four corners of each of a top plate 2b and a bottom plate 2a are cut and chamfered sections 2d are formed, and an inner flap 3 is folded in two stages along the chamfered section 2d and a corner surface 5 is provided at each of corners. While a corner cut carton 1 having such a structure is being formed, a canned beverage C is housed and packaged in a carton. The caser includes: a molding roller 16 removable between a projecting position at which the roller projects to a conveyance area for conveying the carton 1 so that it may be brought into contact with the corner surface 5 of the carton 1 on a conveyor 11 and a retreating position at which the roller is retreated to the side of the conveyor 11 in a manner to retreat the outside of the conveyance area; and a corner surface formation mechanism 15 provided with a spring 23 for urging the molding roller 16 to the projecting position.