Disclosed are an arc extinguishing unit and an air circuit breaker comprising the same. The present disclosure provides an arc extinguishing unit, including: 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 grid cover located above the grid and covering the grid, wherein the grid includes a grid leg extending downward from both ends in the width direction so that an induced magnetic field can be formed by an arc generated when a fixed contact and a movable contact are spaced apart.