A charging unit is disclosed capable of reducing undue variation and fluctuation margin of a charging gap, and controlling accurately the proper gap durably over the change of environmental conditions, which is suitably incorporated into an image forming apparatus. The charging unit is configured to charge an image bearing member in a non-contact arrangement, including a charging roller provided with a core shaft, a charging member formed of electroconductive resin integrally disposed on the periphery of the core shaft, and gap holding members formed of insulating resin each disposed at respective ends of the charging member outside an image forming region. The control of the charging gap is feasible by either forming the gap with a charging member having such a materials condition as to satisfy the relation, |G.sub.30-G.sub.10|.times.5