In access control models, a transaction is allowed to read and write an object only if access rights to read and write the object are granted, respectively. Suppose a transaction reads data d from a file object and then writes the data d to another file object . Here, another transaction can get the data d by reading the file object even if is not granted a read right on the file object . Here, information in the file object flows to the transaction via the file object . We have to prevent illegal information flow to occur by transactions manipulating objects. The role-based access control (RBAC) model is widely used in various applications like database systems. In our previous studies, the legally precedent relation from a role to a role is defined. However, even if the legal condition is satisfied, there is case illegal information flow occurs. In this paper, we redefine legal and illegal precedent relations among roles. In order to check if a collection A of roles illegally precedes a collection B of roles, we introduce a new condition which uses maximal roles of A and B.