Active control effects of self-excited chatter occurring in a turning process have been investigated from the simulation aspects, by utilizing Merritt's modeling method for a machine strucure and the adaptive tracking control techniques developed by Ambrosino, et al. The followings have been obtained. The delay of the control start time, at which the total system is changed from an open loop system into a closed one, hardly affects the vibration control effects, while the larger size of the error sphere (llνll =p) lowers the adaptive tracking performance due to increasing unstable regions. There is also an optimal δopt to minimize the tracking errors in the continuous function cont(ν) =ν/ (llνll +δ). Furthermore, it is found that the control scheme adopted here shows the better robustness against a fairly largeness of parameter variation and modeling error, as compared with that of the LQ control system.