The decision, or object of this research, indicates that the Supreme Court takes the position of set-off expression-of-will theory regarding effect of set-off in case where a set-off of a credit fulfilling negative prescription under Civil Code Art.495 is possible. However, it is proper that, in that case, the Court should take theories of natural set-off and effect of recognition of set-off defense. The object of this research considers complete the effect of deposit of payment pursuant to decision with sentence of provisional execution when the decision of the Court is settled. However, even this situation is appropriate to be recognized as payment under compulsory execution because the deposit of payment pursuant to decision with sentence of provisional execution is payment to evade compulsory execution. In addition, defense of set-off should be allowed to credit fulfilling negative prescription because the Supreme Court has held that defense of set-off is allowed after decision is settled and the set-off can be a reason for claim objection. Then, if a set-off defence at a subsequent suit after the settled precedent suit turns the situation back to the time when a set-off is possible, compulsory execution of the holding regarding the precedent suit shall never be allowed. Although the compulsory execution procedure has been finished, unjusst enrichment should be returned. With the reasons mentioned beforehand, it is argued that the object decision of the Supreme Court under this research is inappropriate.