To provide a technology that ensures satisfactory development over a long period of time by decreasing frictional force produced in the position of the contact of a developer carrier and a strip-and-supply member, thereby reducing developer deterioration.

The development roller 10 and the strip-and-supply roller 11 are flexible. The hardness of the development roller 10 is higher than that of the strip-and-supply roller 11. The radius of curvature of the strip-and-supply roller 11 when not in contact with the development roller 10 in the position of the contact of the development roller 10 and the strip-and-supply roller 11 is larger than the radius of curvature of the development roller 10 when not in contact with the strip-and-supply roller 11 in the position of the contact.