An image forming apparatus includes a developing device, a drum unit, a side plate, a notch, a turning member and a biasing member. The developing device includes a developing roller. The drum unit includes a photosensitive drum and has a protrusion protruding in an axial direction of the photosensitive drum. Thea side plate faces an end surface of the drum unit in the axial direction. The notch is provided in the side plate. The turning member is capable of turning in a direction protruding into the notch and in a direction separating from the notch. The biasing member biases the turning member in a direction close to the notch. The turning member is pushed back by the protrusion inserted into the notch from above, and when the protrusion reaches a bottom of the notch, the turning member presses the protrusion against the notch by a load containing a downward component.