제646조 임차인의 부속물매수청구권 규정의 입법목적은 임차인 보호와 사회경제적 효용에 있다고 보여 진다. 즉 전통적인 사회적 약자라고 할 수 있는 임차인을 보호하기 위한 배분적 정의와 부속물을 당해 임차물로부터 분리함으로써 발생하는 사회경제적 비용을 최소화 하기위한 경제적 효율성을 고려한 입법으로 볼 수 있다는 것이다.
그런데 제646조의 모법이라 할 수 있는 일본의 구 차가법 제5조가 임의규정으로 된 점, 서구 여러 나라의 경우 건물임차인에게 별도로 우리와 같은 부속물매수청구권을 인정하지 않고 있는 점, 제646조 부속물과 제626조 유익비가 본질적으로 차이가 없으며 현실적으로도 그 구별이 애매하여 통일적으로 규율될 필요성이 있는 점 등을 고려할 때 임차인을 보호하기 위해서 굳이 제646조만을 편면적 강행규정으로 할 필요가 있는지 의문이다. 또한 많은 경우에 임의규정은 사실상 강행규정화하고 있는 것처럼 보인다.
본고에서는 제646조가 임의규정으로 된 경우에도 그 입법목적이 달성될 수 있는지를 살펴보았다.
Basically, the contract part, that is, §527 to §733 in the Korean Civil Code is governed by the principle of freedom of contract that includes the freedom to fix contract terms as the contract parties wish. Accordingly, most of the legal rules of the contract part of the Korean Civil Code are supplementary, not mandatory, legal rules that their application could be excluded by contract parties. However, there is social demand that a lessee as a traditionally second-class citizen should be protected, and thus considering this demand, Article 652 provides that any agreement entered by the lease contract parties in contravention of the provisions of Articles 627, 628, 631, 635, 638, 640, 641, and 643 through 647 which is unfavorable to either the lessee or sub-lessee shall be void. Therefore, now, Article 646 is a mandatory legal rule.
According to Article 646, if the lessee of a building or any other structure has attached an accessory to such a building, etc. with the consent of the lessor for the benefit of the lessee’s use, the lessee may demand that the lessor purchase such an accessory at the time when the contract of lease terminates. Article 646 shall apply to the accessory purchased from the lessor, too. By the way, if an accessory becomes a part of the building concerned, the lessee can exercise his or her right to demand cost reimbursement from Article 626, a supplementary legal rule, but if not so, the lessee can exercise his or her right to demand the purchase of accessory from Article 646. Like this, in theory, we can draw a clear distinction between the lessee’s right to demand cost reimbursement of Article 626 and the lessee’s right to demand the purchase of accessory of Article 646. However, in practice, it is not easy to differentiate between the lessee’s right to demand cost reimbursement of Article 626 and the lessee’s right to demand the purchase of accessory of Article 646. For this reason, it seems to be desirable to unify both of them. Besides, the Japanese Housing Lease Act Article 5, a so-called mother law of the Korean Civil Code Article 646, has already been turned from a mandatory legal rule to a supplementary legal rule in 1992. In addition, there is not any legal rule like our Article 646 in western countries, including Germany.
Considering these regards, I'd maintain that Article 646 should be turned from a mandatory legal rule to a supplementary legal rule.