A servo control apparatus includes a speed command generation unit, a torque command generation unit, a speed detection unit, a speed control loop, a speed control loop gain setting unit, a sinusoidal disturbance input unit which applies a sinusoidal sweep to the speed control loop, a frequency characteristic calculation unit which estimates the gain and phase of a speed control loop input/output signal from output of the speed control loop when a sine wave is input to the speed control loop, a reference characteristic generation unit which generates frequency characteristics for a feed axis, and a gain adjusting unit which adjusts the speed control loop gain. The gain adjusting unit uses the reference frequency characteristics and actually measured frequency characteristics to calculate an evaluation function value for each frequency sweep, and adjusts online the speed control loop gain to achieve a desired evaluation function value.