A developing device comprising: a developing roller; a developer conveying unit comprising 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; a developer discharge unit extending from the developer conveying unit in the longitudinal direction of the developing roller and including a developer discharge port to discharge excess developer; an air discharge port 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; and an internal circulation path provided between the developer conveying unit and the developer discharge unit and connecting the developing chamber to the stirring chamber to form an air passage, wherein the air discharge port is to open in a circulation path forming housing forming the internal circulation path, wherein the air discharge port comprises a first air discharge port extending beyond the internal circulation path and toward the developer discharge unit and is inclined in the longitudinal direction and a second air discharge port to open in an outer wall forming the internal circulation path, and the filter comprises first and second filters (330-2, 330-3) located in the first and second air discharge ports (310-2, 310-3), respectively. a developing roller; a developer conveying unit comprising 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; a developer discharge unit extending from the developer conveying unit in the longitudinal direction of the developing roller and including a developer discharge port to discharge excess developer; an air discharge port 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; and an internal circulation path provided between the developer conveying unit and the developer discharge unit and connecting the developing chamber to the stirring chamber to form an air passage, wherein the air discharge port is to open in a circulation path forming housing forming the internal circulation path, wherein the air discharge port comprises a first air discharge port extending beyond the internal circulation path and toward the developer discharge unit and is inclined in the longitudinal direction and a second air discharge port to open in an outer wall forming the internal circulation path, and the filter comprises first and second filters (330-2, 330-3) located in the first and second air discharge ports (310-2, 310-3), respectively.