A developing system includes a developing unit, a mixing container, a rotary feeder, an air pump, and an airflow regulator. The developing unit is configured to convert a latent image into visible form using a developer. The mixing container is separated from the developing unit and is configured to hold and mix part of the developer after use. The rotary feeder is configured to dispense the developer from the mixing container to a delivery path. The air pump is configured to supply compressed air to deliver the dispensed developer to the developing unit through the delivery path. The airflow regulator is located where the rotary feeder connects to the delivery path, and is configured to prevent the compressed air from flowing toward the rotary feeder from the delivery path.