A cartridge detachably mountable to an apparatus main unit of an image forming apparatus, the apparatus main unit including a photosensitive drum and a portion-to-be-contacted, the cartridge comprising: a developing agent bearing member rotatable about an axial line and configured to supply developing agent to the photosensitive drum; a plurality of electric contacts (13f, 15f, 47a) each configured to be electrically connected to the apparatus main unit; and a positioning portion configured to contact with the portion-to-be-contacted of the apparatus main unit so that a position of the cartridge, with respect to the apparatus main unit in a direction orthogonal to the axial line, is determined; wherein assuming that a region, which is surrounded by a plurality of straight lines (S1, S2, S3, S4) and edges of the electric contacts (13f, 15f, 47a), is formed on a projection plane orthogonal to the axial line so as to satisfy first, second, and third conditions, an entirety of a positioning region (Uy) is located inside the region when viewed in the axial line, the positioning region (Uy) being a region of the positioning portion configured to contact with the portion-to-be-contacted of the apparatus main unit when the cartridge is mounted to the apparatus main unit,wherein the first condition is that each of the ends of the plurality of straight lines (S1, S2, S3, S4) is situated at an edge of the electric contacts (13f, 15f, 47a) or at a center of the developing agent bearing member, wherein the second condition is that the center of the developing agent bearing member is situated at an intersection of the plurality of straight lines (S1, S2, S3, S4), or upon one of the straight lines (S1, S2, S3, S4), and wherein the third condition is that each of the straight lines (S1, S2, S3, S4) is stipulated so that the area of the region is maximal, within the constrictions of the first and second conditions. a developing agent bearing member rotatable about an axial line and configured to supply developing agent to the photosensitive drum; a plurality of electric contacts (13f, 15f, 47a) each configured to be electrically connected to the apparatus main unit; and a positioning portion configured to contact with the portion-to-be-contacted of the apparatus main unit so that a position of the cartridge, with respect to the apparatus main unit in a direction orthogonal to the axial line, is determined; wherein assuming that a region, which is surrounded by a plurality of straight lines (S1, S2, S3, S4) and edges of the electric contacts (13f, 15f, 47a), is formed on a projection plane orthogonal to the axial line so as to satisfy first, second, and third conditions, an entirety of a positioning region (Uy) is located inside the region when viewed in the axial line, the positioning region (Uy) being a region of the positioning portion configured to contact with the portion-to-be-contacted of the apparatus main unit when the cartridge is mounted to the apparatus main unit,wherein the first condition is that each of the ends of the plurality of straight lines (S1, S2, S3, S4) is situated at an edge of the electric contacts (13f, 15f, 47a) or at a center of the developing agent bearing member, wherein the second condition is that the center of the developing agent bearing member is situated at an intersection of the plurality of straight lines (S1, S2, S3, S4), or upon one of the straight lines (S1, S2, S3, S4), and wherein the third condition is that each of the straight lines (S1, S2, S3, S4) is stipulated so that the area of the region is maximal, within the constrictions of the first and second conditions.