An optical scanner for an image forming apparatus has a housing having a wall surface provided with a through-hole, and an optical scanning unit, which is provided within the housing, scans light on an object to be scanned in order to form an image on the object to be scanned, and includes: a polygon motor; a polygon mirror that reflects the light while being rotated by a driving force of the polygon motor; a mirror member that reflects the light reflected by the polygon mirror, toward a target object; and a mirror holding member that is attached to the wall surface of the housing and holds the mirror member. The mirror holding member has a heat radiation part that is exposed to the outside of the housing through the through-hole.