PURPOSE: To maintain electrostatic charging characteristic which is not only initially stable but also stable even with the lapse of time by constituting an electrostatic charging roller of a conductive mandrel and a thin film with which the surface of the mandrel is coated and which has specified volume resistivity value as for the electrostatic charging roller which is allowed to abut on a belt-like photosensitive body so as to electrostatically charge the surface of the photosensitive body.

CONSTITUTION: The electrostatic charging roller 17 which is allowed to abut on the belt-like photosensitive body 14 so as to electrostatically charge the surface of the photosensitive body 14 is constituted of the conductive mandrel and the thin film with which the surface of the mandrel is coated and whose volume resistivity value is 103-109Ω. Namely, the roller 17 is constituted of hard material such as SUS (a stainless steel). Therefore, permanent deformation is prevented from being caused by pressure from the outside. When the roller 17 abuts on the photosensitive body 14, the abutting part shows surface-contact, so that the contact area of nip width L is secured and an angle θ can be adjusted, thereby maintaining stable electrostatic charging characteristic.