A beam spot controlling method for controlling the beam-converging position by a light beam from an objective lens on a recording track of a recording medium comprising the steps of (a) rotating a tapered prism having an inclination-imparting portion capable of imparting an inclination to a light beam which enters the tapered prism for changing the inclination of the light beam incident on said objective lens for controlling the beam-converging position by the light beam; (b) causing a light beam to enter the tapered prisms; and (c) causing the light beam exiting from the tapered prism to enter the objective lens, and directing the exiting light beam onto the recording track of said recording medium, and an apparatus for performing the above beam spot controlling method.