1. Revocation of the judgment of the first instance, and the plaintiff (Counterclaim defendant)'s claim on the principal lawsuit is dismissed.

2. The Defendant (Counterclaim Plaintiff) raises an objection.

1. The reasoning for this court’s judgment is the same as the corresponding part of the judgment of the court of first instance, and thus, this is acceptable in accordance with the main sentence of Article 420 of the Civil Procedure Act.

2. Judgment on the plaintiff's main claim

A. The Plaintiff’s assertion that the Plaintiff notified the Defendant of the payment of the remainder under the instant sales contract, but the Defendant failed to perform its obligation to pay the remainder, thus the Plaintiff’s rescission of the instant sales contract by serving a duplicate of the instant complaint.

In addition, the defendant expressed his intention not to perform the obligation to pay the balance to the plaintiff, and the plaintiff may rescind the contract without the peremptory notice of performance, thus cancelling the contract of this case.

Therefore, the Defendant is obligated to pay the Plaintiff penalty of KRW 100 million equivalent to the down payment pursuant to Article 6 of the instant sales contract.

B. 1) Determination 1) In a bilateral contract, both parties who are in a quid pro quo relationship are in principle related to the simultaneous performance, and those who intend to rescind a contract on the grounds of the other party’s non-performance in a bilateral contract with a simultaneous performance relationship provide for the other party to perform his/her own obligation. When the other party’s act is required in performing his/her obligation, he/she shall complete a preparation to perform at any time, notify the other party of his/her intention and notify the other party of his/her receipt so that he/she may result in the delay of performance. The mere preparation for the performance is not sufficient (see, e.g., Supreme Court Decision 2008Da94646, 94653, Mar. 26, 2009). In cases of rescission of a contract due to the cancellation of a contract by default, the other party’s peremptory notice and provision for self-performance in a concurrent performance relationship is not required (see, e.g., Supreme Court Decision 2008Da94653, Sept. 14, 14, 19