An image forming apparatus is disclosed which includes a housing, one or more drum cartridges, and one or more exposure heads. Each of the one or more drum cartridges includes a photoconductor drum and is installable in the housing. Each of the one or more exposure heads is configured to expose a corresponding photoconductor drum to light, and to be movable between an exposure position fit to expose the corresponding photoconductor drum to light and a retreated position away from the corresponding photoconductor drum. The housing has a groove through which to guide installation of the drum cartridge and in which to cause an exposure head in a corresponding exposure position to be located in place in a sub scanning direction.