Japanese has three sets of demonstratives: ko-series (nearer to the speaker), so-series (nearer to the hearer; moderately away from the speaker), α-series (far from the speaker). The theory that the use of so depends on the relative operability of interlocutors was examined. Thirty college students were tested in two conditions: in finger-pointing condition (a control condition), the experimenter asked questions pointing referents, in which subjects answered using demonstratives ; in pointer-pointing condition, the experimenter questioned using a 120 cm long pointer enhancing her operability. First hypothesis was that subjects' use of so would be greatest when the distance from subjects to the referent was relatively long but that from the referent to the experimenter was considered as relatively short. The second one was that subjects' use of so would be higher under the pointer-pointing condition than under the finger-pointing one. The results confirmed these hypotheses.