Article 20, paragraph 1, subparagraph 6, of the Estate and Gift Tax Law providing that property given as a gift by and between husband and wife does not count in the total gift amount is a provision of tax exemption for mutual gifts between persons having a legal marriage. Companions of opposite-sex who, due to deficiency in meeting legal requirements, have not formed a legal marriage are not entitled to the same tax treatment. Since the above-mentioned provision is designed to preserve legally formed marital relation, the purpose is legitimate and the method used is helpful to maintaining marriage institution, it cannot be said to have violated the principle of equality guaranteed by Article 7 of the Constitution.

　　　 The principle of equality declared by Article 7 of the Constitution is not an absolute, mechanic equality in form. In stead, it is designed to guarantee equality in substance for the people in their the legal standing. Article 19 of the Constitution provides that the people shall have the duty to pay tax according to the law. However, if the law makes an exception or a special provision to lessen or to relieve certain persons from tax burden when specified conditions are met, and the discrimination has a legitimate cause, it does not violate the principle of equality (see J.Y. Interpretation No. 565 and No. 635).

　　　 Article 20, paragraph1, subparagraph 6, of the Estate and Gift Tax Law providing that property given as a gift by and between husband and wife does not count in the total gift amount is a provision of tax exemption for mutual gifts between persons having a legal marriage. Becuse the classification is based on the existence of a legally formed marital relation, the gift tax exemption is a discriminatory tax treatment. In view of the fact that gift tax collection involves redistribution of the nation’s financial resources, and is closely related to the promotion of public interests and the implementation of national policy, the Legislature does have more discretion in shaping the content of this subject matter. Therefore, if the provision at issue has a legitimate purpose, and the criteria for classification and the discriminatory method used also bear a rational relation to this purpose, it is consistent with the principle of equality.

　　　 The disputed provision for tax exemption for transfer of property rights between husband and wife is a policy that the Legislature has deliberately made in light of the difficulty in distinctively separating the commingled spousal properties necessary　for the livelihood of the family. The law is designed to preserve the marriage institution, and the purpose is a legitimate one. Where a married person who conjugated with a third party outside the wedlock, even with a subjective intent to live together with such third party like a married couple and the objective fact of having cohabited and shared the livelihood for a long time, he/she has violated the monogamous marriage and jeopardize the economic interests of his/her spouse. Therefore, the provision at issue is not an arbitrary statute enacted by the Legislature. Since it has a rational relation to the maintenance of marriage institution, it does not contradict the equality principle of Article 7 of the Constitution.

　　　 Although those unmarried companions of opposite sex with a subjective intent to live together like a married couple and the objective fact of cohabitation do not have a matrimonial relation in law, the relationship between them is very much similar to the relationship of legally married husband and wife, and the provision at issue, which does not provide for gift tax exemption for mutual gifts between such companions, would seem susceptible to a doubt of violating the principle of equality provided that there is in addition a fact of longtime sharing of the livelihood between such couples. However, the Legislature has prescribed registration and monogamy requirements as conditions for the validity of a marriage. The purpose is to strengthen the effect of public notice, to preserve ethics and social order, and to promote public interest. This is constitutionally legitimate. Although the provision at issue exempts gift tax only for legally married couples, yet this is for consideration of preserving marriage institution. The purpose is legitimate and the method used is helpful to maintaining marriage institution. It cannot be said that the act has contradicted the principle of equality. As for those cohabited companions with similarity to a legal marriage, the Legislature may, taking into considerations the constitutional protection of fundamental rights of the people as well as changes in the social condition and cultural development, give them adequate legal protection to the extent not disparaging marriage institution and other public interests. It is so pointed out apropos.