A developing device includes: a casing that has a housing part, an upstream edge and a downstream edge, and a rectangular opening that opposes a development region, the rectangular opening being provided between the upstream and downstream edges; a cylindrical developer conveying body to rotate in a state of passing the rectangular opening, the cylindrical developer conveying body conveying the developer to the development region; and a flexible sheet member that has an upstream end part and a downstream end part, the upstream end part being fixed at the downstream edge of the casing, the downstream end part being a free end and coming into contact with a layer of the developer in a rotation axis direction of the developer conveying body at a position of the developer conveying body which passes the downstream edge of the opening.