In a line head, a plurality of light emitters are arrayed on a substrate in a first direction. Each of the light emitters is operable to emit a light beam. In a rod lens array, a plurality of rod lenses are arrayed in the first direction, and each of the rod lenses is adapted to focus the light beam emitted from an associated one of the light emitters onto a target surface. The substrate and the rod lens array are attached to a holder elongated in the first direction. Positioning members are provided at both end portions of the holder in the first direction. A relative position between the substrate and at least one of the positioning members is variable in a second direction perpendicular to the first direction.