A technical problem is to fully make up for a restricted upper limit to the preform body wall thickness. An object is to provide a bottle which is narrow-mouthed and yet has a substantially expanded body. The molding process comprises steps of: (1) injection molding a preform in the shape of a test tube taller than the bottle wherein the preform has a cylindrical mouth opening portion disposed in an upper part of the preform, and wherein the mouth opening portion of the preform serves also as a mouth opening portion of the bottle product; (2) thermally shrinking the preform from an initial height so that portions other than the mouth opening portion of the preform would have a height that is smaller than that of the bottle; and (3) setting this thermally shrunk preform in a blow mold and biaxially drawing and blow molding the preform into the bottle.