To make the size increase of a developing device to be less likely, and to reduce the manufacturing cost, while reinforcing a regulating blade so that assembly accuracy can be maintained.

The developing device is provided with the regulating blade 4, capable of regulating the thickness of a developer layer formed on the peripheral surface of a developing roller 3 proximately to the peripheral surface of the developing roller 3. A reinforcing member 9, whose rigidity is lower than that of the regulating blade and which is in series nearly over the entire length of the regulating blade, is applied on the side of one side surface 8 of the regulating blade and is fixed with a plurality of machine screws so as to be integrated.

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