1. The defendant (Counterclaim plaintiff)'s appeal is dismissed.

2. The defendant-Counterclaim plaintiff raised in the trial is dismissed.

A principal lawsuit and a counterclaim shall be deemed simultaneously.

1. Basic facts

A. The Plaintiff is a person who operates a gas station (hereinafter “instant gas station”) under the trade name, “C gas station” on the ground outside B, and one parcel of land, in the period of harmony.

B. The Defendant was supplied by the Plaintiff with oil equivalent to KRW 48,814,560 in total from July 2014 to November 14, 2014 while performing civil engineering works at the construction site of a chemical D apartment near the gas station in the instant case.

[Ground of recognition] Facts without dispute, Gap evidence 1, Eul evidence 2 (including branch numbers, hereinafter the same) and the purport of the whole pleadings

2. The assertion and judgment

A. The summary of the argument 1) The Defendant of the main lawsuit did not pay KRW 11,263,834 out of the oil price to the Plaintiff. Thus, the Defendant of the main lawsuit sought payment of the said oil price. 2) The counterclaim Defendant traded with the Plaintiff in the manner of deducting the oil price supplied after paying the Plaintiff the amount of KRW 15 million as the advance payment of the oil price and then deducting the amount of the oil price supplied.

The amount of oil paid by the Defendant to the Plaintiff, including the aforementioned advance payment, is KRW 52,315,893, and the amount of oil supplied by the Plaintiff to the Defendant is merely KRW 48,814,560. The Plaintiff is obligated to return the excess amount of oil paid to the Defendant as unjust enrichment.

B. Of the total amount of KRW 52,315,893 claimed by the Defendant as the prepaid payment, the Plaintiff deposited KRW 15 million into the Plaintiff’s account designated by F, not for the repayment of the oil price, but for the Plaintiff’s deposit of KRW 15,00,000,00 in total under the name of lease deposit and rent, when concluding a lease agreement on the said land to use the land on the land of Nonparty F, Inc. (hereinafter “F”) located in the vicinity of the construction site, the Defendant, not for the payment of the oil price.