An attempt has been made to show that the possibility of the "method of constant sum" as a psychological measurement in study of quality. For the purpose of comparison with the "method of paired comparison" and "method of constant sum" a typical experiment that shows the relation between the "definition" and "distance from microphone" was carried out for both methods. As a result, we could see the fact that (1) the result of method of constant sum is evaluated in a small error as order of method of paired comparison, (2) the correlation coefficient between both scales is 0. 998, (3) the errors of individuals are a small order opposite to expectation, (4) the result of consideration of internal consistency is very good. Furthermore, (5) in the field of application (the study of quality with the psychological scale) the method of constant sum has little limitation compaired with the method of paired comparison. (6) But for the subjects, special training which means the ability of numerical fractionation is required careful process.