Arc extinguishing unit and air circuit breaker comprising same

An air circuit breaker, comprising:

• a fixed contact;
• a movable contact moved in a direction toward or away from the fixed contact;
• and
• an arc extinguishing unit positioned adjacent to the fixed contact and the movable contact, and configured to extinguish an arc generated when the fixed contact and the movable contact are spaced apart,
• wherein the arc extinguishing unit comprises:
• side plates spaced apart from each other and disposed to face each other;
• a plurality of grids disposed between the side plates, spaced apart from each other, and coupled to the side plates, respectively;
• and
• a magnet unit forming a magnetic field for changing a path of an arc formed between a fixed contact and a movable contact disposed to be spaced apart from the fixed contact, and disposed adjacent to the outermost grid adjacent to the fixed contact among the plurality of grids.