The lower court rejected the Defendant’s defense that, in concluding the instant agreement on the ground of fraud or mistake, there was no evidence to acknowledge that the Plaintiff deceptioned the remaining building-to-land ratio of the instant building on the ground that the floor area (69.4m2) exceeds the remaining building-to-land ratio on the side of the Plaintiff, and that the remaining building-to-land ratio on the part of the Defendant (Counterclaim Plaintiff; hereinafter “Defendant”) to the extent that the excess amount is reduced. The Plaintiff, despite being well aware of such circumstance, knew the Defendant A (hereinafter “Defendant”) who withdrew from May 27, 2005 without notifying the Plaintiff of the fact. The Plaintiff, despite being aware of such circumstance, did not know of the above circumstances, knew the Plaintiff’s defense that the instant agreement was cancelled on the ground of fraud or mistake, it could not be deemed that the Plaintiff had known the remaining building-to-land ratio on the ground that not only the total floor area of each of the instant building, but also the remaining building area of each of the instant building could not be seen as the specific building-to-land ratio.

In light of the records, the court below's measure is just and acceptable, and there is no error of law such as misunderstanding of facts against the rules of evidence, misunderstanding of the reasoning, or misunderstanding of legal principles as to mistake of declaration of intention, etc.

2. As to the counterclaim

According to the records, the defendant filed a preliminary counterclaim in preparation for the plaintiff's claim to be accepted, and the first instance court rejected all the plaintiff's principal lawsuit and the defendant's counterclaim on the ground that there is no interest in the lawsuit, and the lower court appealed only the plaintiff's appeal against the judgment of the first instance court, which is limited to the scope of the judgment of the lower court as to the claim of the principal lawsuit, and did not make any judgment

However, the defendant's preliminary counterclaim is sought on the condition that the claim of the principal lawsuit will be accepted, and as long as the first instance court rejected the plaintiff's claim of the principal lawsuit, the defendant's preliminary counterclaim cannot be subject to the judgment of the first instance court, and as such, the first instance court decided on the lawsuit which cannot be subject to the judgment, it shall be null and void (see Supreme Court en banc Decision 98Da2253 delivered on November 16, 200, etc.). Thus, the defendant's preliminary counterclaim cannot be subject to the judgment of the court below solely on the ground that the defendant did not file an appeal against the counterclaim dismissed in the first instance court. Accordingly, the court below should have judged it by taking the defendant's preliminary counterclaim as subject to the judgment, as long as it accepted the plaintiff's appeal and accepted the plaintiff's claim of the principal lawsuit.

Nevertheless, the court below did not make any decision on the defendant's preliminary counterclaim on the grounds as stated in its reasoning. Thus, the court below erred by misapprehending the legal principles on the preliminary counterclaim, and it is obvious that such illegality affected the judgment.

3. Conclusion

Therefore, the part concerning the counterclaim among the judgment below is reversed, and that part of the case is remanded to the court below for a trial and determination, and the remaining appeal is dismissed. It is so decided as per Disposition by the assent of all participating Justices on the bench.

Justices Kim Ji-hyung (Presiding Justice)