a first light guide part reflecting and guiding a light emitted from a light source;

a polygon mirror configured to be rotatable and including a plurality of reflective parts, the reflective parts being arranged to form a regular polygonal reflective surface when viewed in a rotation axis direction, the polygon mirror reflecting the light guided by the first light guide part by the reflective part while rotating;

a second light guide part reflecting the light reflected by the reflective part of the polygon mirror and guiding the light so that the light is irradiated to an irradiation target at each of the reflective parts; and

an adjustment part adjusting a position of an optical axis of a light incident on the polygon mirror in the rotation axis direction by changing at least one of a position and an orientation of an optical component included in the first light guide part,

wherein the reflective part of the polygon mirror is configured to reflect the incident light so that the optical axis of the incident light offsets in the rotation axis direction,

wherein the adjustment part moves the optical component in parallel to adjust the position of the optical axis of the light incident on the polygon mirror in the rotation axis direction, thereby changing a position of the light irradiated on the irradiation target in a line width direction of the light, the irradiation target is irradiated with the light while a position of the light irradiated on the irradiation target in the line width direction, and

wherein, while the light is offset and reflected by the reflective part, an optical path length of the light is substantially constant regardless of an amount of offset of the incident light.