The purpose of this study was to examine whether a contract, in which the consumer's intention was distorted due to intervention of other party in the consumer's deceleration of intention process based on the principle of private freedom or the principle of freedom of contract, is in effect. The revision of the Japanese civil law in 2017 has an implications for this agenda. The Japanese civil law revised in 2017 stated that the declaration of expression by incompetent person is invalid and stipulated the principle of freedom of contract. In particular, the specification of incompetent person was to reflect the reality that legal disputes over the presence or not of mental capacity is occurring in the social situation of aging acceleration. This seems to be a shift of the concept from 'abstract' to 'individual and concrete' person. In addition, in order to expand the regulations on deceleration of intention, the Japanese Civil Code newly established the rules for mistake in motive established by case theory, and also reviewed the establishment of a regulation on 'misrepresentation' as a type of mistake in motive. Although the regulation on 'misrepresentation' was not included in the revision, the discussion on the establishment of this clause provides an implication regarding the case in which an declaration of intention through a motive caused by the other party is revoked.