A support structure comprises a pair of mounting members and a pair of connecting members, which are joined together by a joining member. The image reading unit is mounted on the top surfaces of the mounting members. The connecting members are disposed vertically, and the respective mounting members are supported on the top ends of the connecting members in a cantilevered manner. Securing portions are formed on each of the connecting members in the vicinity of the bottom end thereof at at least two locations vertically spaced apart from each other. The support structure is integrally secured to the paper feed unit via the securing portions of the connecting members, and the image reading unit integrally moves together with the support structure according to the horizontal movement of the image forming unit and the paper feed unit. Accordingly, the image reading unit does not fall off the support structure.