In an image forming apparatus, a drum supporting member has a pair of opposed sidewalls facing in an axial direction of a plurality of photoconductor drums, and supports the plurality of photoconductor drums at insides of the sidewalls. A sheet output tray portion is formed in an upper wall of a casing of the apparatus as a downwardly recessed portion to receive a recording sheet with an image formed thereon. Part of the drum supporting member is disposed in spaces formed inside the casing at both sides of the sheet output tray portion facing in the axial direction of the plurality of photoconductor drums. The part of the drum supporting member overlaps the sheet output tray portion as viewed in the axial direction.