A person who without any legal ground derives a benefit from the property or services of another and thereby causes loss to the latter shall be bound to return such benefit.

If a person has discharged an obligation with the knowledge that no such obligation has ever existed, he may not demand the return of the subject matter.

If an obligor has discharged an obligation which is not due, he may not demand the return of the subject matter：Provided, That if the obligor discharges such obligation by mistake, the obligee shall return the benefit which he received therefrom.

In the event that a person, not liable to an obligation, has discharged such an obligation by mistake and such discharge conforms to a sense of morality, he may not demand the return of the subject matter.

(1) If, in the event that a person other than the obligor has discharged an obligation by mistake, the obligee has in good faith destroyed evidentiary documents, relinquished any security, or lost his claim rights by prescription, the person who has effected the performance may not demand the return of his payments.
(2) In the case of paragraph (1), the person who has effected the performance may avail himself of the right to obtain reimbursement from the obligor.

If a person granted property or rendered service for an illegal cause, he may not demand the return of benefits resulting therefrom：Provided, That this shall not be the case if such illegal cause exists only on the part of the person enriched.

(1) If the person enriched is unable to return the object itself which he has received, he shall return the value of the object.
(2) When the person enriched is unable to return the benefit, a third party acting in bad faith, who has obtained the object or the benefits gratuitously from the person enriched, shall be liable to return such objects in accordance with the provisions of paragraph (1).

(1) The person enriched in good faith shall be liable to act as set forth in Article 747 to the amount that he still possesses of such benefits.
(2) A person enriched in bad faith shall return the benefits received by him together with interest, and if there has been any damage, he shall be bound also to make compensation.

(1) If the person enriched becomes aware of the fact that no legal ground had ever existed after he had received such benefit, he shall be liable to return the benefit as a person enriched in bad faith, from the time of his awareness of the above fact.
(2) The person enriched in good faith shall, if defeated in a lawsuit, be deemed to be a person enriched in bad faith from the time such action was filed.