An image forming apparatus includes a controller configured to perform operations including: controlling an exposing unit to expose a first ratio to a full scan width and thus to form a first exposed section, and to expose a second ratio smaller than the first ratio thus to form a second exposed section, controlling a detecting member to acquire: a first voltage in a case where a first test current flows in the first exposed section; a second voltage in a case where the first test current flows in the second exposed section; a third voltage in a case where a second test current larger than the first test current flows in the first exposed section; and a fourth voltage in a case where the second test current flows in the second exposed section; and identifying the photosensitive member based on the first to fourth voltages.