An information recording and/or reproducing apparatus for recording data onto and/or reproducing data from a recording medium by irradiating a light beam emitted from a light source onto a desired track of the recording medium through an optical system. The apparatus includes (i) a single processor for executing an input/output control of the data for the apparatus and a servo process of the light beam such that the input/output control of the data and the servo process of the light beam are alternately switched at a predetermined period, and (ii) an actuator for moving the light beam on the basis of the servo process of the processor. The precision of the servo process is changed so that the precision is increased when an amount of an external disturbance is large.