In accordance with this study, the following conclusion has been obtained by introducing the SN technique into evaluation of the abrasive grinding of magnetic disk substrate and examining the reasonability to use characteristics value for determining an optimum machining condition. (1) It is found that evaluation of an optimum machining condition according to the minimizing characteristics, aiming characteristic and maximizing characteristic is controlled by the confidence limit and error to the confirmation test islconsiderably small where the evaluation is applicable as an evaluation characterisitc value.(2)The optimum machining condition determined by the evaluation characteristic value gives the result enabling to explain and examine well the phenomena caused by the conditional changes of respective control factors. (3) By means of the evaluation characterisitc value proposed, the scale of action effect of each factor is converted to a value, which can be judged quantitatively.