A developing device frame unit for supporting a regulating member for regulating a layer thickness of a developer on a developer carrying roller, said developing device frame unit comprising: a developing device frame having a seal forming portion; one end sealing member which is provided at one end of said developing device frame in an axial direction of said developer carrying roller and which is contactable to a surface of said developer carrying roller to prevent the developer from leaking in the axial direction of said developer carrying roller when said developer carrying roller is mounted; the other end sealing member which is provided at the other end of said developing device frame in the axial direction of said developer carrying roller and which is contactable to the surface of said developer carrying roller to prevent the developer from leaking in the axial direction of said developer carrying roller when said developer carrying roller is mounted; a blade sealing member for sealing between said regulating member and said developing device frame to prevent the developer from leaking when said regulating member is mounted, wherein said blade sealing member is an elastomer resin material which is injection-molded with a metal mold and which is provided in said seal forming portion where said one end sealing member and the other end sealing member are provided, said blade sealing member connecting said one end sealing member and the other end sealing member with each other; and a protrusion (94a, 94b) provided by squeezed-out portion of the elastomer resin material, wherein the squeezed-out portion is provided by injecting, into a space defined by said metal mold, said seal forming portion, said one end sealing member and the other end sealing member, a volume of the elastomer resin material larger than a volume of the space so as to flow out of the space in a buffer portion (101, 102) being connected to said seal forming portion and to form the squeezed-out portion. a developing device frame having a seal forming portion; one end sealing member which is provided at one end of said developing device frame in an axial direction of said developer carrying roller and which is contactable to a surface of said developer carrying roller to prevent the developer from leaking in the axial direction of said developer carrying roller when said developer carrying roller is mounted; the other end sealing member which is provided at the other end of said developing device frame in the axial direction of said developer carrying roller and which is contactable to the surface of said developer carrying roller to prevent the developer from leaking in the axial direction of said developer carrying roller when said developer carrying roller is mounted; a blade sealing member for sealing between said regulating member and said developing device frame to prevent the developer from leaking when said regulating member is mounted, wherein said blade sealing member is an elastomer resin material which is injection-molded with a metal mold and which is provided in said seal forming portion where said one end sealing member and the other end sealing member are provided, said blade sealing member connecting said one end sealing member and the other end sealing member with each other; and a protrusion (94a, 94b) provided by squeezed-out portion of the elastomer resin material, wherein the squeezed-out portion is provided by injecting, into a space defined by said metal mold, said seal forming portion, said one end sealing member and the other end sealing member, a volume of the elastomer resin material larger than a volume of the space so as to flow out of the space in a buffer portion (101, 102) being connected to said seal forming portion and to form the squeezed-out portion.