A lens array unit focuses the light emitted from light emitting elements on the photoconductive drum. A longitudinally extending lens array includes a plurality of lenses and projections. The lenses are aligned in a row substantially perpendicular to optical axes of the lenses. The projections are disposed on both sides of the row, and extend outwardly further than the lens surfaces to protect the lens surfaces of the plurality of lenses. A light shielding member includes a mounting portion that holds the lens plate and a light shielding portion that shields part light passing through the lenses.