Legitimacy is defined as evaluated approvability of others’ or self rights to manage commons on the basis of some reasons or values. The present study proposed ‘Who & Why Game (W2G)’ for the purpose of examinations of mutual approval structure among various actors and providing a training game to let participants consider about the legitimacy. The results of W2G and its revised version, W2GII, indicated that judgments of legitimacy on rights for managing commons to be changed by discussions among actors, and at the same time, their recognition of its change was also suggested as an educational effects. Moreover the results of W’GII revealed the process of consensus by discussing on judging legitimacy of each actor according to their involvement to commons. It was discussed on potential applicability of W2G in both an experimental tool on the legitimacy of public policies for management of commons, and an educational training game to experience the process of making consensus on mutual approval for rights.
