An image forming apparatus includes an air communication port, and an outer casing covering an outside of a frame member of the image forming apparatus. The outer casing includes a first side surface facing in one of a first direction and a second side surface facing in one of a second direction perpendicular to the first direction. The first side surface includes a first surface portion extending in a vertical direction, a second surface portion offset in the first direction from the first surface portion toward the inside of the image forming apparatus, and a third surface portion connecting the first and second surface portions. The third surface portion is provided with the air communication port penetrating the outer casing. The first, second surface and third surface portions extend to the second side surface.