Disclosed herein is a focal length adjustment apparatus in which a magnetic fluid that serves as attenuation means is injected between a magnet and a coil to achieve an improvement in a magnetic flux density and damping effect. The apparatus comprises a moving unit including a lens barrel that contains at least one lens therein, and a coil arranged on an outer circumference of the lens barrel, a fixed unit including a yoke formed with an opening for receiving the lens barrel, a case into which the yoke is inserted and mounted, and a magnet affixed to the yoke to be arranged adjacent to the coil, a supporting member used to elastically support the moving unit relative to the case, and attenuation means interposed between the coil and the magnet to attenuate vibration of the moving unit.