Relative pronoun that is one of the important relative pronouns but we have an impression that its scope of use has been somewhat narrowed. In the light of history of relative pronouns relative pronoun toot has the longest history of all relative pronouns and it was widely used even in Middle English and early Modem English. On The other hand, we can see that the relative use of that has been gradually weakened as the relative pronouns who and which has expanded their scope of use. It is quite natural that the scope of use of toot as a relative pronoun has been narrowed as who is mainly used in referring to person and which is mainly used in referring to things. And we can note that that is used only in restrictive clauses, not in nonrestrictive clauses, for that has a strong characteristics of relative conjunction in comparing with who and which. That as a relative pronoun still has its own weight because it can take an antecedent referring to person and thing. In particular, it is general tendency that who is used more frequently than that in the case of referring that it is not adequate for that to refer to things. In contrast, who has an advantage over that because the former originally refers only to person.