the variation of deviations of actual positions of a moving body from corresponding command positions is quantitatively evaluated as a servo control error , whether a feedback control system is oscillating is decided on the basis of the servo control error , set values of parameters expressing characteristics of a closed loop or a control element included in the feedback control system are adjusted on the basis of the result of the decision whether the feedback control system is oscillating , and the values of the parameters are adjusted to optimum values slightly different from values which will cause the feedback control system to oscillate .