The invention relates to a numerical control (NC) device, and provides a servo control device that displays, by a two-dimensional image, evaluation of control precision of a servo system, and that can adjust the servo system according to a visual method, and provides a method of adjusting the servo system. The control device includes: an instruction unit that instructs a position instruction having periodicity; a unit that records a track of position data based on a position feedback of a servo system according to the position instruction; and a first drawing unit that draws position data based on the position feedback, data before a quarter cycle or after a quarter cycle of the position data or position data based on the position instruction before a quarter cycle or after a quarter cycle, on a two-dimensional plane including orthogonal two axes, as the axis data of the orthogonal two axes respectively.