A developing device includes a housing, a developing roller, and a blade. The housing includes a developer chamber and an opening. The developing roller is disposed in the developer chamber, such that a part of the developing roller in a rotational direction thereof is exposed to an outside of the opening. The developer roller includes a sleeve rotatable around a shaft and a magnetic element. The magnetic element has a magnetic polarity opposite to that of a developer and is disposed at an entrance rotational position of the developer roller at which a sleeve region of the sleeve goes into the developer chamber from the outside of the opening. The blade is positioned near a surface of the sleeve to regulate a thickness of the developer on the surface of the sleeve. The thickness of the developer regulated on the sleeve region at the entrance rotational position by the blade is equal to or greater than 0.6 mm and equal to or less than 1.4 mm.