A developing unit, comprises: a conveying shaft; a developing conveying portion conveying a developer in an axial direction as the conveying shaft rotates; a discharge opening discharging the developer from the inner wall surface; an accumulating chamber accumulating the discharged developer; and an opening/closing member opening and closing the discharge opening due to its own weight as the rotating body rotates, and being in an open state at the developing position, an opening/closing fulcrum of the opening/closing member being at a lower end portion of the opening/closing member at the developing position, the developing unit being held at a rotating body, and successively being made to oppose a developing position of an image carrier due to rotation of the rotating body.