A divider plate for two or more inlet ports provided in a cylinder head of an internal-combustion engine comprises divider portions that divides inside of the two or more inlet ports along an intake air flow, a side cast-in insert portion provided on at least one side portion located in a direction perpendicular to that of the intake air flow, that is enclosed by molten metal during casting of the cylinder head, an inner cast-in insert portion that is provided between the divider portions, that is enclosed by the molten metal during the casting of the cylinder head, and an inner accelerator formed in the inner cast-in insert portion, accelerates coagulation of the molten metal, wherein the inner accelerator has at least one of a plurality of holes, a concave portion, a convex portion, and a concave-convex portion, or a combination of a hole and a concave portion, a convex portion or a concave-convex portion.