In our society, it is a major issue to enhance cooperative behavior. Without this, our society fall into social dilemma situations, and gets worse and worse. Such a situation in a organization leads to violation of social rules, and at the worst case it suffers from serious accidents or scandals. Therefore, it is very important for organizational managers to make efforts and take measures to enhance cooperative behavior. Although there seem to be many ways to constantly elicit cooperative behavior, the punishment is one of the most effective measures for enhancing cooperation. This study focused on the effects of penalty and probability of punishment on the cooperation, and getting insight into how punishment strategy should be used to get rid of social dilemmas and enhance cooperation. This study conducted two simulation experiments to find the optimal penal regulations condition that can suppress violations (defective behavior) in a 2-person Prisoner's dilemma situation. The effects of probability of punishment and penalty on the cooperative behavior were identified with the interactive effect of both experimental factors. The defect (no-cooperative behavior) decreased when the punishment penalty was heavy and the probability of the defect revealing was low than when the punishment penalty was light and the probability of the defect revealing was high.