An optical device including: a laser light emitting portion that emits laser light; a polygon mirror having a reflective surface that reflects the laser light, the polygon mirror being driven to rotate and deflecting the laser light emitted from the laser light emitting portion; a first lens through which the laser light reflected by the polygon mirror is transmitted, the first lens refracting the laser light; a second lens through which the laser light having passed through the first lens is transmitted, the second lens refracting the laser light; and an adjustment unit that adjusts at least one of a length of a first optical path between the polygon mirror and the first lens, and a length of a second optical path between the first lens and the second lens.