An air circuit breaker comprising: an upper cover that includes a space therein; a fixed contact; a movable contact that is positioned adjacent to the fixed contact, and is moved in a direction toward or in a direction away from the fixed contact; an arc extinguishing unit that is positioned adjacent to the fixed contact to extinguish an arc extending from the fixed contact toward the movable contact; and a cover magnet unit that is coupled to the upper cover and is positioned adjacent to the fixed contact to form a magnetic field for applying an electromagnetic force to the arc, characterized in that the upper cover includes: a first upper cover that covers the fixed contact at one side of the fixed contact opposite to the movable contact and includes a space therein to accommodate a portion of the arc extinguishing unit and the fixed contact; and a second upper cover that is coupled to the first upper cover, is positioned on the other side of the fixed contact facing the movable contact, and includes a space therein to accommodate remaining portions of the arc extinguishing unit and the movable contact, wherein the cover magnet unit is coupled to any one of the first upper cover and the second upper cover, and extends toward the other one of the first upper cover and the second upper cover. an upper cover that includes a space therein; a fixed contact; a movable contact that is positioned adjacent to the fixed contact, and is moved in a direction toward or in a direction away from the fixed contact; an arc extinguishing unit that is positioned adjacent to the fixed contact to extinguish an arc extending from the fixed contact toward the movable contact; and a cover magnet unit that is coupled to the upper cover and is positioned adjacent to the fixed contact to form a magnetic field for applying an electromagnetic force to the arc, characterized in that the upper cover includes: a first upper cover that covers the fixed contact at one side of the fixed contact opposite to the movable contact and includes a space therein to accommodate a portion of the arc extinguishing unit and the fixed contact; and a second upper cover that is coupled to the first upper cover, is positioned on the other side of the fixed contact facing the movable contact, and includes a space therein to accommodate remaining portions of the arc extinguishing unit and the movable contact, wherein the cover magnet unit is coupled to any one of the first upper cover and the second upper cover, and extends toward the other one of the first upper cover and the second upper cover. a first upper cover that covers the fixed contact at one side of the fixed contact opposite to the movable contact and includes a space therein to accommodate a portion of the arc extinguishing unit and the fixed contact; and a second upper cover that is coupled to the first upper cover, is positioned on the other side of the fixed contact facing the movable contact, and includes a space therein to accommodate remaining portions of the arc extinguishing unit and the movable contact, wherein the cover magnet unit is coupled to any one of the first upper cover and the second upper cover, and extends toward the other one of the first upper cover and the second upper cover.