A peel-openable package (10A, 10B, 10C, 10D), comprising: a package main body having a content enclosed therein, the package main body including: a main body portion forming a cavity having a periphal portion and a lid welded to the peripheral portion and closing the cavity, the lid including an inner sheet member located at a position corresponding to an inner portion of the package main body; and an outer film member bonded to a surface of the inner sheet member, the surface corresponding to an outer portion of the package main body; wherein: the inner sheet member and the outer film member have a foldable portion in an area thereof where the inner sheet member and the outer film member are bonded together; the foldable portion includes a peel region where the inner sheet member and the outer film member are allowed to be peeled off from each other; characterized in that the foldable portion includes a cutout (21, 31), in the peel region, in each of the inner sheet member and the outer film member, the cutouts (21, 31) extending so as to cross a direction corresponding to a folding direction in which the foldable portion is folded, and the cutouts (21, 31) each being formed into an opening running in a thickness direction when the foldable portion is folded; the cutout formed in the inner sheet member and the cutout formed in the outer film member are away from each other by a predetermined interval, the predetermined interval extending in the direction corresponding to the folding direction; and facing surfaces of the inner sheet member and the outer film member facing each other are bonded together by an adhesive layer provided between the facing surfaces such that the facing surfaces are peelable from each other, the facing faces being defined in at least the peel region. a main body portion forming a cavity having a periphal portion and a lid welded to the peripheral portion and closing the cavity, the lid including an inner sheet member located at a position corresponding to an inner portion of the package main body; and an outer film member bonded to a surface of the inner sheet member, the surface corresponding to an outer portion of the package main body; an inner sheet member located at a position corresponding to an inner portion of the package main body; and an outer film member bonded to a surface of the inner sheet member, the surface corresponding to an outer portion of the package main body; wherein: the inner sheet member and the outer film member have a foldable portion in an area thereof where the inner sheet member and the outer film member are bonded together; the foldable portion includes a peel region where the inner sheet member and the outer film member are allowed to be peeled off from each other; the inner sheet member and the outer film member have a foldable portion in an area thereof where the inner sheet member and the outer film member are bonded together; the foldable portion includes a peel region where the inner sheet member and the outer film member are allowed to be peeled off from each other; characterized in that the foldable portion includes a cutout (21, 31), in the peel region, in each of the inner sheet member and the outer film member, the cutouts (21, 31) extending so as to cross a direction corresponding to a folding direction in which the foldable portion is folded, and the cutouts (21, 31) each being formed into an opening running in a thickness direction when the foldable portion is folded; the cutout formed in the inner sheet member and the cutout formed in the outer film member are away from each other by a predetermined interval, the predetermined interval extending in the direction corresponding to the folding direction; and facing surfaces of the inner sheet member and the outer film member facing each other are bonded together by an adhesive layer provided between the facing surfaces such that the facing surfaces are peelable from each other, the facing faces being defined in at least the peel region.