The U.S. Supreme Court delivered a decision on the case between AT&T and Concepcion, which confirmed the contractuality of a defense as a threshold to distinguish between what is a viable defense for invalidation of consumer arbitration agreement and what is not. In this paper, the adhesiveness of arbitration clause, which is a unique character for consumer arbitration, is investigated in the U.S. as a legal defense to invalidate the consumer arbitration agreements, and its contractuality and related legal doctrines are analyzed. The legal issues of consumer arbitration have been analysed in several legal perspectives including the voluntary, knowing and intelligent doctrine, doctrine of separation, contract of adhesion and the contractuality of defenses. Among all of these, the first three issues are related with arbitration clause, and the last one, the contractuality of defenses, reflects the nature of defenses invalidating the consumer arbitration agreement.