An image forming apparatus includes an optional device, a casing, an image forming section and a sheet conveyor device. The optional device performs optional processing. The image forming section is located inside of the casing and forms an image on a sheet. The sheet conveyor device conveys, to the optional device, the sheet with an image formed thereon by the image forming section. The optional device and the casing are fixed to each other. The sheet conveyor device is fixed to the optional device and the casing.