An exposing device includes a light-emitting element array including plural light-emitting elements disposed in a first direction and a second direction orthogonal to or substantially orthogonal to the first direction, a lens array including plural lenses that focus lights from the light-emitting elements, a supporting member that supports the light-emitting element array and the lens array, and an exposure-position adjusting mechanism including a rotation adjusting unit that rotates the supporting member around or substantially around an axis in the first direction.