An image forming apparatus includes: a casing, a first process cartridge including a first photosensitive drum and a first drum-cleaning unit configured to collect waste toner on the first photosensitive drum, a second process cartridge including a second photosensitive drum and a second drum-cleaning unit configured to collect waste toner on the second photosensitive drum, a cartridge-supporting body movable between an internal position inside the casing and an external position outside of the casing, a conveying unit conveying the waste toner collected by the first and second drum-cleaning units, and a waste toner cartridge accommodating the conveyed waste toner. The casing includes a first positioning plate receiving one end portion of the first and second process cartridges, and a second positioning plate receiving another end portion of the first and second process cartridges. The conveying unit is disposed between the first positioning plate and the second positioning plate.