A light deflector is disclosed that includes a movable mirror serving as a deflector supported by a rotary shaft and configured to deflect a light beam emitted from a light source and scan an area to be scanned; a rotation part configured to cause the movable mirror to vibrate in a reciprocating manner by periodically applying a rotational torque to the movable mirror; a driving circuit configured to control the rotation part; a circuit board having the driving circuit provided thereon, the circuit board being configured to support the movable mirror as a unit; a contact plane contacting the circuit board in a plane perpendicular to the rotary shaft of the movable mirror; and a positioning part configured to determine the position of the rotary shaft in the contact plane.