A developing device includes: a developer supporter that includes: a magnet member that has a plurality of magnetic poles; and a cylinder member; and a thickness regulation member wherein, of the plurality of the magnetic poles, a magnetic pole, which is placed at a position nearest to the thickness regulation member downstream in a rotation direction of the cylinder member from the thickness regulation member, has a maximum position of a normal magnetic flux density distribution, and the maximum position is placed outside the area of angle α downstream in the rotation direction of the cylinder member from the thickness regulation member, and wherein the diameter of the cylinder member is D, the projection width is W in a case where the thickness regulation member is projected onto the surface of the cylinder member, and the angle α is 180×W/(D×π).