The present research investigated the legitimacy of actors that participate in managing natural resources as commons, and the determinants of their legitimacy. Legitimacy was defined as the approvability of the rights of others and the self, to participate in the management of the commons. Traits that actors expected of managers were highlighted as the determinants of legitimacy. We examined the effects of three traits: expertise, partyship, and locality. A questionnaire survey targeted three actors-farmers, fishermen, and other workers-involved in the red clay flow problem that has damaged the local sea in Ginoza village, in Okinawa. As a result, the legitimacy of farmers and fishermen was higher than that of civil servants. Results also indicated that the parties to the problem were more favored as managers than the experts, and that the actors favored local community members as managers over experts. Furthermore, the favored traits of managers as determinants of legitimacy were inconsistent among the actors. These suggested that the subjective locations of actors in participating in the control of the red clay flow were different from each other. The contributions of these findings to the expansion of social governance in managing the commons are discussed.