A laser beam reflected off a polygon mirror travels below a beam portion and is reflected off a reflection mirror. The laser beam reflected off the reflection mirror is emitted through an opening formed directly below the beam portion. The beam portion is provided above the opening through leg portions. With the structure, the rigidity on the periphery of the opening can be ensured. Supporting portions for supporting the reflection mirror are reinforced by reinforcing portions, so that the reflection mirror is prevented from being vibrated. In addition, the reflection mirror is supported such that the reflection mirror does not contact the beam portion. Even when the beam portion is vibrated, the vibration is not conveyed from the beam portion to the reflection mirror.