An electrophotographic image forming apparatus may include a main body including a reference protrusion having a reference surface on one side and a pressing member on the other side, and a photosensitive member unit configured to move between an operational position and an outer position. The photosensitive member unit stops at a particular position located between the outer position and the operational position. The reference surface of the main body may contact the photosensitive member unit located in the operational position. The pressing device of the main body may be configured to press the photosensitive member unit toward the reference surface when the photosensitive member unit is located in the particular position and in the operational position.