Developing device, image supporter unit, and image formation apparatus

A developing device comprising:

• a developer supporter that includes:
• a magnet member that has a plurality of magnetic poles;
• and
• a cylinder member that is placed on the outer periphery of the magnet member, and that rotates pre se, the developer supporter supporting a developer on a surface of the cylinder member;
• and
• a thickness regulation member that has a cylindrical shape, that is made of a magnetic material, that is placed facing the surface of the cylinder member with a predetermined spacing, and that regulates the thickness of the developer deposited on the surface of the cylinder 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 of the normal magnetic flux density distribution 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).