An optical scanning unit may include a light source unit configured to emit a light beam, an optical housing configured to receive and support the light source unit, an optical device configured to deflect the light beam and to focus the light beam on a light receiving member, and a fixing member configured to fix the light source unit to the optical housing by applying pressure to the light source unit, wherein the pressure is applied in a direction, which is substantially perpendicular to an optical axis direction of the light source unit.