An object of this invention is to provide a gain adjusting method in a servo control device to suppress changes according to a place where a machine is located.This invention provides a gain adjusting method for a servo control device providing speed control of inputting a difference between speed feedback supplied from a servo motor and a command value to output a torque command, characterized in that after a speed loop gain is increased to detect vibration at each of points moved over a movable range of a machine, the speed loop gain is decreased to detect the gain when the vibration becomes still as a maximum value, thereby providing a set gain value corresponding to a machine.