The developing device includes a developing roller, a developer conveying unit, a developer discharge unit, and an air discharge port. The developer conveying unit includes a developing chamber provided with the developing roller and extending in a longitudinal direction of the developing roller, a stirring chamber arranged in parallel to the developing chamber, and a barrier wall having a first communication port and a second communication port, at respective ends in the longitudinal direction, to connect the developing chamber with the stirring chamber. The developer discharge unit extends from the developer conveying unit in the longitudinal direction of the developing roller and includes a developer discharge port to discharge excess developer. The air discharge port is to house a filter to filter a developer, the air discharge port being provided between the developer conveying unit and the developer discharge unit to discharge air in the developer conveying unit.