An actuator used with an optical pickup includes: a base on which a holder is fixed; a lens holder in which a plurality of installation holes are formed such that a plurality of objective lenses to record and/or reproduce optical discs having different recording densities are installed at different heights; a support member, which movably supports the lens holder, having one end coupled to the lens holder and the other end coupled to the holder; and a magnetic circuit which drives the lens holder in focusing and tracking directions. The plurality of installation holes include a first installation hole in which a first objective lens for at least one type of low density optical disc is installed, and a second installation hole in which a second objective lens for a higher density optical disc than the low density optical disc is installed. When a working distance of the first objective lens for the low density optical disc installed in the first installation hole is represented as WD1, and a working distance of the second objective lens for the high density optical disc installed in the second installation hole is represented as WD2, the first and second installation holes are provided so that the first and second objective lenses are installed to satisfy the Equation: WD1>WD2, a separation distance between the optical disc and the second objective lens=WD2+.alpha., where, .alpha.=IWD1-WD2|.times.(0.1-1.0). The second installation hole is located in a more outer circumference of the optical disc than the first installation hole.