Image forming apparatus including a rotary member and a detecting member which detects light from the surface of the rotary member

An image forming apparatus, comprising:

• a rotary member, which is endless and movable, and is configured to bear a toner image directly on a surface of the rotary member or via a recording material;
• a detecting member configured to detect light from the surface of the rotary member;
• and
• a controller configured to acquire information relating to a position on the rotary member in a moving direction of the rotary member based on a detection result obtained by the detecting member,
• wherein the rotary member has a plurality of grooves along the moving direction on the surface of the rotary member with respect to a width direction of the rotary member perpendicular to the moving direction, and has, with respect to the moving direction, a first area and a second area having a shorter length in the moving direction than the first area, the first area and the second area being different from each other in friction coefficient with respect to the width direction, and
• wherein the controller acquires the information relating to the position on the rotary member in the moving direction based on a result of detecting, by the detecting member, light from the surface of the rotary member including at least the second area with respect to the moving direction.