A two-dimensional array include N light-emitting arrays each formed of M light-emitting units arranged equally spaced along a direction T tilting from a main scanning direction at an angle α toward a sub-scanning direction. The light-emitting arrays are equally spaced in the sub-scanning direction. A space ds2 between light-emitting arrays with respect to the sub-scanning direction satisfies ds2=ds1×M where ds1 is a positional difference in the sub-scanning direction between light-emitting units which are adjacent each other in the main scanning direction and orthographically-projected on a virtual line extending in the sub-scanning direction. The angle α satisfies α=sin−1((ds2/d1)/M) where d1 is a space between light-emitting units in the light-emitting array with respect to the direction T. The space ds2 is equal to the space d1.