To extend the service life of a bag and to effectively use resources by changing easily the corner parts of the front and rear bodies of the bag by new parts even when the corner parts wear to discolor or deform.

Corner pads which are closely fitted and joined to the corner parts formed at four corners of the lower side of the outer surface of the bag by the front body, the rear body and through gussets of the bag are molded integrally and three-dimensionally so that they are fitted closely to the flat surfaces of the bodies forming the corner parts the bag and to curved surfaces formed by the through gussets abutting on the flat surfaces of the bodies, and adhesive tapes (of a male type) are sewn on the closely fitted surfaces, while adhesive tapes (of a female type) are sewn respectively on the flat surfaces of the bodies forming the corner portions of the bag and the curved surfaces formed by the through gussets abutting on the flat surfaces of the bodies, which are opposite to the closely fitted surfaces. The corner pads and the bag are joined together by an adhesivity between the adhesive tapes (of the male type) and those (of the female type) and thus removal of the pads is enabled.