The present invention relates to an image forming apparatus in which a sheet cassette for containing sheets is removably mounted to a body of the apparatus. The image forming apparatus comprises a frame structure having a pair of legs spaced apart from each other, a bottom plate arranged on the legs, a first side plate arranged at one ends of the legs and uprightly mounted on the bottom plate, a second side plate arranged in confronting relation to the first side plate at the other ends of the legs and having a lower end portion extending below the legs and covering the other ends of the legs, and stay members for interconnecting the first and second side plates at their upper portions.