An apparatus includes a first-computation unit computing first-angular-velocity-instruction values for driving first-and-second-rotation units to track a moving object, using a detected tracking error and a detected angles, when the moving object exists in a first range separate from a zenith by at least a preset distance, a second-computation unit computing second-angular-velocity-instruction values for driving the first-and-second-rotation units to track the moving object and avoid a zenith-singular point, using the detected angles, the detected tracking error and an estimated traveling direction, and a control unit controlling the first-and-second-rotation units to eliminate differences between the first-angular-velocity-instruction values and the angular velocities when the moving object exists in the first range, and controlling the first-and-second-rotation units to eliminate differences between the second-angular-velocity instruction values and the angular velocities when the moving object exists in a second range within the preset distance from the zenith.