Aberrations are sufficiently corrected, and an excellent image is acquired. Provided is a variable-focus optical system including a positive-power front-group optical system, a rear-group optical system having the same power, and an optical-system driving unit configured to relatively change the distance therebetween in the optical axis direction, wherein the front-group optical system consists of a positive-power first-group optical system formed of a joined lens, that is, a lens L1 and a lens L2, a positive-power second-group optical system consisting of a lens L3, and a third-group optical system formed of a lens L4 and a lens L5, and the rear-group optical system consists of a positive-power fourth-group optical system formed of a lens L7 and a lens L6, a fifth-group optical system consisting of a positive-power lens L8, and a positive-power sixth-group optical system formed of a joined lens, that is, a lens L10 and a lens L9.