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The setoff is an extinguishment of an obligation by declaration of intention. In general one party declares intention of extinguishment of an obligation, and the obligation is extinguished in same amount. But exceptionally obligation is extinguished without declaration of intention for setoff. It is so called ‘ipso jure compensatio’ in French. The setoff without declaration of intention is very convenient for each party. But a third party who wants to attach the claim cannot have opportunity for execution. Because the claim is extinguished before third party exercises his claim. So I think the setoff without declaration of intention has some problems, and it should be restricted for a third party. In case of lease security deposit is paid by tenant. In Korea the amount of security deposit is numerous, the creditor of tenant attach the security deposit. But landlord always takes precedence of creditor of tenant. Landlord do not execute his claim, until the amount of claim becomes more than the amount of security deposit, then the creditor of tenant cannot do anything for performance of his claim. So the right of landlord to security deposit must be restricted. In case of payment of advance, I sustain the judicial precedent. Payment of advance can be extinguished without declaration of intention, there is no problem in principle of law. In case of deposit certificate, judicial precedent prohibits setoff in some cases. But deposit always become object of declaration of intention by bank. Therefore bank offset claim and deposit preferentially; a third party who wants to attach deposit cannot attain his purpose. Although setoff is very useful system, a third party takes disadvantage in some cases. So for advantage of a third party, I think restriction of setoff is needed.