To unnecessitate or simplify the special sealing of a fine hole caused by anodic oxide coating applied to a developing roller.

Sand blast treatment is performed to the surface of the developing roller 4 coming into contact with a photosensitive body 2 so as to form ruggedness thereon, and further the anodic oxide coating treatment is applied to the surface of the roller 4 on which the ruggedness is formed. The particle diameter of the free additive 3b of non-magnetic one-component toner 3 is set to be smaller than the diameter of the fine hole made by the anodic oxide coating treatment. Therefore, the additive 3b of the toner 3 easily enters and is embedded in the fine hole made by the anodic oxide coating treatment, and the sealing treatment of the fine hole is automatically performed by the additive 3b. Thus, the special sealing treatment is unnecessitated or simplified because it is assisted by the sealing treatment by the additive 3b.