Image forming apparatus for determining the positional relationship between an exposing means and the surface of a photosensitive body

An image forming apparatus, comprising:

• a photosensitive body;
• an exposing unit which exposes a surface of the photosensitive body to form an electrostatic latent image on the surface of the photosensitive body;
• a developing unit which attaches a developer to the electrostatic latent image to form a developer image corresponding to the electrostatic latent image formed on the surface of the photosensitive body;
• a carrier body, which is moved through a portion opposite to the photosensitive body and onto which the developer image formed on the photosensitive body is to be transferred;
• a mark forming unit which controls the exposing unit to form a mark made from the developer image on a surface of the carrier body;
• a light sensor which senses light reflected by the carrier body;
• an edge detector which senses edges of the mark formed on the surface of the carrier body based on an output of the light sensor;
• and
• a deciding unit which decides a positional relation between a focal point of the exposing unit and the surface of the photosensitive body based on the detected edge detected by the edge detector.