Abstract
In investigating how set-off defenses matter in arbitration, one should take into account that it is not permitted against the parties' will for arbitrators to rule on the disputes that are not the subject of an arbitration agreement, unless otherwise agreed upon by the parties involved, because it is considered that the parties intend to solve only the disputes which are the subject of the agreement by arbitration. Also, one should keep in mind that the parties must settle the disputes that are the subject of an arbitration agreement by arbitration when they conclude the agreement, and it is not allowed against the parties' will to resolve the disputes in other ways. The parties may agree whether the respondent can request for arbitration on the counterclaim, which is his/her claim against the claimant, and whether the respondent can raise a plea for a set-off that his/her claim against the claimant is a counter obligation. Failing on such agreement, the respondent may submit a counterclaim when his/her claim and the claimant's claim are the subject of the same arbitration agreement. The arbitral tribunal may rule on the counter obligation when the arbitration agreement, which becomes the basis for the claimant' claim, has an effect on the counter obligation. Where the claimant fails to raise an objection even after he/she becomes aware that the respondent has requested for arbitration or has raised a plea for set-off by providing his/her claim which is not the subject of the arbitration agreement as a counterclaim or a counter obligation, the arbitral tribunal may rule on the respondent's claim against the claimant. On these occasions, the arbitral tribunal has to guarantee the parties an opportunity to defend themselves by pointing out those situations. It will meet the purposes of arbitration systems to rule out the jurisdiction of the courts when the plaintiff alleges the existence of the arbitration agreement, in case the respondent raises a plea for set-off based on his/her claim which is not the subject of the arbitration agreement in the litigation procedures. However, where the plaintiff fails to allege the existence and conducts pleading in the court with regard to the counter obligation, the court must not reject the respondent's set-off defense because of the existence of the agreement.