A developing apparatus includes a housing, a developing roller, a supply roller, and a thickness regulating member. The housing is configured to accommodate developer that includes developer particles having a mean volume diameter. The developing roller is rotatably supported in the housing and has a peripheral surface configured to carry the developer. The supply roller is rotatably supported in the housing, contacts the developing roller, and configured to supply the toner to the developing roller. The thickness regulating member includes a contact member contacting the peripheral surface. The contact member is configured to regulate a thickness of the developer on the peripheral surface such that an average of the thickness of the developer on the peripheral surface becomes smaller than or equal to the mean volume diameter.