Role-based Access Control(RBAC) model has advantage of easy management of access control with constraints such as permission inheritance and separation of duty in role hierarchy. However, previous RBAC studies could not properly reflect the real-world organization structure with its role hierarchy. User who is a member of senior role can perform all permissions because senior role inherits all permissions of junior roles in the role hierarchy. Therefore there is a possibility for senior role members to abuse permissions due to violation of the least privilege principle. In this paper, we present a new model of role hierarchy, which restricts the unconditional permission inheritance. In the proposed model, a role is divided into sub roles(unconditional inheritance. restricted inheritance, private role), keeping organization structure in corporate environment. With restricted inheritance, the proposed model prevents permission abuse by specifying the degree of inheritance in role hierarchy