A developing device frame unit supporting a regulating member regulating the layer thickness of developer on a developer carrier. The unit includes a frame having a seal forming portion, first and second, first and second end seals contactable to the carrier surface to prevent carrier-axial-direction leaking of the developer, and a blade sealer sealing between the regulating member and the frame to prevent developer leaking when the regulating member is mounted. The blade sealer is an elastomer resin material which is injection-molded with a metal mold and in the seal forming portion where the end seals are provided. The blade sealer connects the end seals with each other, and a protrusion provided by a squeezed-out portion of the resin material is provided by injecting, into a space defined by the metal mold, the seal forming portion, and the end seal seals, a resin material volume larger than a volume of the space.
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