1. As to whether the Defendant is obligated to purchase the program use right (ground of appeal No. 3)

In light of the circumstances stated in its holding, the court below acknowledged the court below's decision that the defendant did not perform its duty of free evaluation of evidence on August 22, 2008 regarding the service contract (hereinafter "the service contract in this case") concerning the maintenance and repair of the Korea and the Navy Data Processing System (hereinafter "KNDS") on August 22, 2008 and the period from August 22, 2008 to August 21, 2009, as the program installed in the NANDS, and did not perform its duty of free evaluation of evidence against logical and empirical rules issued by the United Kingdom International HS JBBS (hereinafter "JBS"), or did not perform its duty of free evaluation of evidence for the purpose of maintaining and using the program from 200 to 200.68 of 209 to 200.68 of 208.

2. As to whether a claim for return of unjust enrichment can be filed with the Defendant (ground of appeal No. 1 and No. 2)

A. In a case where contractual performance benefits not only the other party to the contract but also a third party, the party who provided the performance may not claim the other party for the return of unjust enrichment from the third party, in addition to claiming the other party to the contract (see, e.g., Supreme Court Decisions 9Da66564, 66571, Aug. 23, 2002; 201Da48568, Nov. 10, 201). This legal doctrine also applies in a case where the performance of the contract is performed by a business management. Accordingly, a person who provided the business for another party without any obligation without any obligation may not claim the return of unjust enrichment from a third party, in addition to claiming the reimbursement of expenses, etc. under the provisions of the Civil Act, as well as the repayment of expenses, etc. under the provisions of the business management under the Civil Act.

B. Based on the circumstances stated in its reasoning, the lower court determined that the Defendant was obligated to return the amount equivalent to the amount of the JTS purchase price for the year 2008 without any legal cause, while the Defendant was selected as the maintenance and repair service provider as above and the Defendant was obligated to purchase at its own expense for the year 2008 JTS use contract with JBS company. In so doing, the Plaintiff obtained profits from the amount equivalent to the amount of the JTS purchase price for the year 2008 without any legal cause, and the Plaintiff suffered damages equivalent to the same amount, and the Defendant was obligated to return it to the Plaintiff in unjust

C. However, we cannot accept the above decision of the court below for the following reasons.

According to the reasoning of the judgment below and the evidence duly admitted by the court below, ① Korea has to obtain the right to use JDS directly or through the KNTS maintenance and repair service company in order to use KNTS lawfully, and Korea has included its duty to purchase the JDS in the KNTS maintenance and repair service contract to be concluded every year through open tendering, ② The plaintiff was from October 18, 2006 to October 17, 2007, and 207 from October 18, 2007 to June 30, 2008, and the plaintiff continued to use the KNTS 208 after the expiration of 208 JS service contract with the plaintiff 20.3rd KNS maintenance and repair service contract with the plaintiff 2 and the plaintiff 2 was not notified of the expiration of 208 J. 29.6, 2008.

Comprehensively taking account of the above facts, the Plaintiff’s contract for the maintenance and repair of the previous KNTS concluded with the Republic of Korea was terminated and the new service company has not yet been selected, and thus, upon entering into a JDS use contract with the JBS company and granted the rights or status as the final user of the JDS in the Republic of Korea. Thus, the Plaintiff’s above act can be deemed to fall under the management of the Republic of Korea for the Republic of Korea. However, even if the Defendant’s separate purchase of the JDS use contract was unnecessary due to the conclusion of the above use contract, it cannot be said that the Defendant would be exempted from the obligation of the Defendant to allow the Republic of Korea to use the JDS program under the service contract of this case, separate from the Plaintiff’s expectation to enter into the service contract of this case and selection of the service company after the purchase of the JS use contract of this case, and thus, it cannot be said that the Defendant’s claim for damages incurred by the Defendant’s use of the program cannot be said to have been made.

Nevertheless, the lower court, based on its stated reasoning, concluded that the Defendant was obligated to return unjust enrichment equivalent to the purchase cost of 2008 portion directly to the Plaintiff. In so doing, the lower court erred by misapprehending the legal doctrine on the claim for return of unjust enrichment, thereby adversely affecting the conclusion of the judgment. The allegation in the grounds of appeal assigning this error is with merit.

3. Conclusion

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 Kim Chang-suk (Presiding Justice)