A developing device for an image forming apparatus of a non-magnetic one-component type. The developing device has a developing roller having a body and a shaft. Bearings for supporting the shaft have a groove made in a contact surface that is in contact with the shaft, and grease is pooled in the groove. The contact surface of the shaft has a surface roughness from 0.2 to 0.5, and the grease has consistency from 265 to 385 ( 1/10 mm·20° C.).