A developing device frame unit for supporting a regulating member for regulating a layer thickness of a developer on a developer carrying member, includes a developing device frame having a seal forming portion; two end sealing members which are provided each at one longitudinal end of the developing device frame and which is contactable to a surface of the developer carrying member to prevent the developer from leaking in an axial direction of the developer carrying member when the developer carrying member is mounted; a blade sealing member 1 for sealing between the regulating member and the developing device frame to prevent the developer from leaking when the regulating member is mounted, wherein the blade sealing member is an elastomer resin material which is injection-molded with a metal mold and which is provided in the seal forming portion where the two end sealing members are provided, the blade sealing member connecting the two end sealing members with each other.
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