In light of the principle of equity, it is reasonable to view that a trucking business operator is in the simultaneous performance relationship with a trucking business operator’s obligation to implement procedures for ownership transfer registration and payment of management fees in arrears for an owner of an automobile. Therefore, if an owner of an automobile continues to operate the trucking service by using the trucking transport business operator’s registered name while the trucking business operator has a right of defense of simultaneous performance and has continued to operate the trucking transport business, barring any special circumstance, the owner of an automobile gains profit equivalent to management expenses stipulated in the above entrusted management contract by running the trucking transport business using the trucking transport business’s registered name without any legal ground. Such profit gained by the owner of an automobile should be returned to the trucking business operator as unjust enrichment (see Supreme Court Decision 2003Da37136, Nov. 28, 2003). The aforementioned obligation of the trucking business operator to return ownership transfer fees to the said owner of an automobile for simultaneous performance of the aforementioned entrusted management contract by 207Da37136, supra.

According to the reasoning of the judgment below and the records, the plaintiff entered into the entrusted management contract of this case with the defendant on August 10, 1998, and completed the transfer of ownership in the name of the defendant on August 10, 1998; the plaintiff terminated the entrusted management contract of this case on March 16, 2009; the copy of the complaint was served on the defendant on March 16, 2009; and on October 13, 2009, "the defendant shall receive KRW 6,010,490 from the plaintiff and simultaneously implement the transfer of ownership registration procedure of this case on December 2, 2009." The plaintiff did not dispute the fact that the plaintiff continued to pay the unpaid management expenses of this case until August 2, 2009, which were recognized as having a concurrent performance relationship with the defendant on December 2, 209, and only paid the unpaid management expenses of this case until the date of payment.

Examining these facts in light of the aforementioned legal principles, when the plaintiff continued to operate the freight truck and operated the freight trucking business, the plaintiff bears the obligation to return unjust enrichment equivalent to the management expenses during the period. Thus, on December 2, 2009, when the plaintiff paid unpaid management expenses up to August 2, 2009, the plaintiff bears the obligation to return unjust enrichment equivalent to the management expenses incurred up to 4 months from the date of the above payment, in addition to the unpaid management expenses until August 2, 2009, which was recognized to have been in the simultaneous performance relationship. Such obligation to return unjust enrichment is also in the simultaneous performance relationship with the defendant's obligation to implement the procedure for registration of transfer of ownership, and even if the plaintiff paid the above unpaid management expenses to the defendant, the defendant still holds the name of the owner of the entrusted automobile with the right of simultaneous performance. Therefore, the plaintiff has the obligation to return unjust enrichment during the period of continuous operation of the freight trucking business after the payment of unpaid management expenses, and the obligation to return unjust enrichment to the defendant's obligation to return the ownership.

In addition, the Defendant’s exercise of the claim for return of unjust enrichment with respect to the Plaintiff’s claim for performance of the transfer registration procedure cannot be deemed as going against the good faith principle.

Nevertheless, the lower court did not examine whether the Plaintiff continued to engage in the same business as the Defendant’s trucking transport business, even after the termination of the instant consignment management contract, and rejected the Defendant’s simultaneous performance defense as to unjust enrichment equivalent to the management expenses from the date of the first instance judgment to the date of the conclusion of the pleadings after rendering a judgment, on the grounds of various circumstances as indicated in its reasoning, on the grounds of the following: (a) even though the Plaintiff fulfilled the obligation to pay management expenses, etc. according to the judgment after the first instance judgment was rendered, it cannot be permitted under the principle of good faith or equity to have the Plaintiff additionally bear the expenses incurred by delay of the transfer of ownership registration for the purpose of additional payment of management expenses from the Plaintiff until the transfer of ownership is registered; and (b) the Defendant’s simultaneous performance defense as to unjust enrichment equivalent to the

Therefore, the judgment of the court below is reversed, and the case is remanded to the court below for a new trial and determination. It is so decided as per Disposition by the assent of all participating Justices on the bench.

Justices Cha Han-sung (Presiding Justice)