A developing device includes a rotator (220) that rotates around a shaft, and a bearing element (223) that supports the shaft to a housing. A sliding element formed of a composite material that contains self-lubricating thermoplastic olefin resin as a base material is used as the bearing element (223). The sliding element formed of the composite material has at least a ratio of numerical values of "Rockwell hardness"/"bending elastic modulus" in a range from 25 to 45, and provides a sliding surface of which a frictional coefficient is lower than that of the sliding element formed of the base material.
