An arc extinguishing unit and an air circuit breaker comprising same are disclosed. An arc extinguishing unit, according to an embodiment of the present disclosure, comprises an extinguishing magnet unit that forms a magnetic field inside the arc extinguishing unit. Accordingly, a generated arc receives an electromagnetic force in the direction facing the exterior of the air circuit breaker, and thus can be rapidly moved and extinguished. The extinguishing magnet unit is accommodated in a magnet case. The magnet case can seal the extinguishing magnet unit. Therefore, the extinguishing magnet unit is not damaged by the generated arc.