Image forming apparatus

An image forming apparatus comprising:

• a photosensitive member unit comprising a rotatable photosensitive member and being attachable to or detachable from the image forming apparatus;
• a charging member configured to contact the photosensitive member and charge a surface of the photosensitive member by applying only a DC voltage;
• an exposing unit configured to expose the charged surface of the photosensitive member to form an electrostatic latent image;
• a developing unit comprising a developer bearing member for bearing developer and configured to develop the electrostatic latent image formed on the photosensitive member;
• an information storage portion provided in the photosensitive member unit and configured to store information with respect to an attenuation amount of a surface potential of the photosensitive member by which the surface potential is attenuating until the photosensitive member rotates from a contact position of the photosensitive member to the charging member to a development position of the photosensitive member facing to the developer bearing member;
• and
• a setting portion configured to set a voltage to be applied to the charging member at a time of image formation before the image formation is started after the photosensitive member unit is attached to the image forming apparatus based on a current value flowing to the charging member in a case where a voltage of a preset voltage value is applied to the charging member, the preset voltage value, and the information with respect to the attenuation amount,
• wherein if the attenuation amount is a first attenuation amount, the setting portion sets an applying voltage to be applied to the charging member at the time of image formation to a first voltage, and
• if the attenuation amount is a second attenuation amount larger than the first attenuation amount, the setting portion sets an applying voltage to be applied to the charging member at the time of image formation to a second voltage larger than the first voltage.