A developing device includes a developer tank configured to contain a developer including a toner and a carrier, the developer tank having a discharge port which is provided in a lateral side surface of the developer tank and configured to discharge the developer, a developing agent supplier configured to develop a latent image by using the toner contained in the developer tank, and a plate-shaped member configured to be formed in a direction of height from a lower end of the discharge port and partially cover the discharge port to regulate the discharge of the developer.