In an image forming apparatus, each of a plurality of exposure units provided at a drum supporting member is configured to be movable between an exposure position in which the exposure unit is located in proximity to a corresponding photoconductor drum supported by the drum supporting member and a retreating position in which the exposure unit retreated away from the corresponding photoconductor drum is positioned by a stopper, such that the exposure unit is located inside the drum supporting member regardless of whether the exposure unit is in the exposure position or in the retreating position. A motion-imparting member is provided at the drum supporting member, movably relative to the drum supporting member and is configured to act on an engageable portion of each exposure unit to thereby cause the exposure unit to move to the exposure position or to the retreating position.