In this paper, some kinds of behavior occurring in the daily life are taken up as examples of the rule-following behavior. If we take a casual glance at them, they seem to be unsystematic and confused. But a close investigation of them will reveal the rules which people follow implicitly to smooth the human relations and to reduce the conflict among them. If it were not for such rules, the strain of human relations would tire people out, because the difficult decision-making is required at any moment in the social situation. People are unaware of them in many cases, but if they are broken, people feel insulted and get angry. For that reason, they are called the implicit rule of social behavior.