A laser condensing optical system of the present invention includes a laser beam source which emits a laser beam, a condensing optical system which is arranged between the laser beam source and a medium and condenses the laser beam in the medium, and a laser divergence point moving unit which can move the position of a laser divergence point of the laser beam along an optical axis of the laser beam in accordance with the refractive index of the medium in which the laser beam is desired to be condensed and the distance from a surface of the medium to a position where the beam is desired to be condensed.