Provided is a developing system including a developing device that includes a replenishing unit that replenishes toner into an accommodating portion of a developer including toner and a carrier, via a replenishing port, a receiving unit that includes a transport member that transports received toner to a discharge port, a connecting member that has an internal space that is formed with an inlet connected with the discharge port and an outlet connected with the replenishing port, and a rotating member that is rotated in the internal space, and includes a blocking surface portion that closes the inlet and the outlet while passing over the inlet and the outlet, and a transport surface portion that receives or discharges the toner while passing over the inlet and the outlet.