Patent ID: 7808519

Claim:
A line head comprising: a microlens array in which a plurality of microlenses having a magnification whose absolute value is below 1 are arranged in a main scanning direction of a surface-to-be-scanned, and a plurality of luminous element groups which are arranged in a one-to-one correspondence with the respective plurality of microlenses, wherein in each of the plurality of luminous element groups, a plurality of luminous elements are arranged at mutually different main-scanning-direction positions in the main scanning direction, the plurality of luminous elements are respectively, caused to emit lights at timings in conformity with a movement of the surface-to-be-scanned in a sub scanning direction, and light beams emitted from the plurality of luminous elements are imaged on the surface-to-be-scanned at mutually different main-scanning-direction positions in the main scanning direction to form a plurality of spots side by side on the surface-to-be-scanned in the main scanning direction, each of the spots having a diameter smaller than that of the respective luminous elements, in each of the plurality of luminous element groups, out of the plurality of luminous elements constituting the luminous element group, two luminous elements caused to emit lights to form adjacent spots are arranged at mutually different sub-scanning-direction positions in the sub scanning direction, out of the plurality of microlenses, two microlenses adjacent to each other in the main scanning direction are arranged at mutually different sub-scanning-direction positions in the sub scanning direction, each of the two microlenses being an inverting optical system, a first and a second luminous element groups are arranged corresponding to the two microlenses respectively, the first luminous element group being located upstream of the second luminous element group in the sub scanning direction and emitting lights earlier than the second luminous element group, and in each of the first and the second luminous element groups, a first and a second luminous elements are arranged at mutually different sub-scanning-direction positions, the second luminous element being located downstream of the first luminous element in the sub scanning direction and emitting light earlier than the first luminous element.