To provide servo controlling method and device capable of performing high-speed control with high accuracy without providing two position detectors for high and low speeds.

In this servo controlling method in which the position of a member which is driven by a servo motor 31 is detected by a position detector 33 and the position information signal for the member to be driven which comprises analog signals detected by the detector 33 is fed back to a servo amplifier 41 to control the servo motor 31, the position information signal is analyzed with low resolution to generate a feedback signal to the amplifier 41 while the member to be driven operates at a speed being higher than a prescribed reference speed, and the position information signal is analyzed with high resolution to generate a feedback signal to the amplifier 41 while the member to be driven operates at a speed being slower than the prescribed reference speed.