A line head, includes: a plurality of luminous elements grouped into a plurality of luminous element groups; and a lens array which includes a plurality of lenses each of which faces the luminous element group, focuses light beams emitted from the luminous element group on an image plane, and accordingly forms a spot group, wherein the plurality of luminous element groups are arrayed in M×N in a first direction and in a second direction which are different from each other, where M and N are integers equal to or greater than two, and spot groups adjacent to each other in a direction corresponding to the first direction are so formed on the image plane as to partly overlap in a direction corresponding to the second direction.