A positional loop gain control method in which a positional control feedback system composed of a speed control circuit (101c), a spindle motor (102), a position coder (104), a fixed-position stop control unit (101e), and a changeover switch (101b), determines the gain of a digital-to-analog converter (301) constituting the fixed-position stop control unit so that the positional loop gain of the positional control feedback system has a set value Kp. When controlling the position at which a spindle stops, the method comprises a step of operating the spindle motor at a predetermined speed Nb, a step of measuring a deceleration time Tf required for the speed of the spindle motor to drop from Nb to zero, and a step of determining a gain KDA of the digital-to-analog converter using the set value Kp, the predetermined speed Nb, the decelaration time Tf, and a distance D between a fixed position and a changeover point at which a speed-control mode is shifted to a position-control mode.