To provide a circuit breaker capable of arc-extinguishing without affecting other portion with simple structure.

One terminal 16 in which a fixed contact 21 mounted at the tip thereof is obliquely incliningly bent in the direction of an air exit 14 is mounted at a case 12 opened with the air exit 14. A contact arm 26 electrically connected to the other terminal 17 arranged at the case 12 via an overcurrent trip device 23 and a linkage 44 is arranged. A moving contact 31 which is contacted with and separated from the fixed contact 21 is arranged at the tip of the side where the contact arm 26 rises and falls. Neighborhood of a connection position between the fixed contact 21 and the moving contact 31 is surrounded by a cylindrical grid holder 82 communicating with the air exit 14. A plurality of arc chute grid 83 is arranged along the direction in which the contact arm 26 rises and falls in the grid holder 82. When the moving contact 31 is separated from the fixed contact 21 by overcurrent between the contacts 21, 31, arc is generated at the tip portion thereof, immediately, the arc is arc-extinguished by the arc chute grid 83.