Provided is a circuit breaker including a single pole breaking unit with a pressure trip device that rotates a trip bar through an arc gas and an opening/closing mechanism unit adjusted to be in a trip state as the trip bar rotates through the pressure trip device. The pressure trip device includes: a first case connected to the single pole breaking unit and having an arc gas discharge hole; a barrier positioned in the front of the arc gas discharge hole and bent through an arc gas discharged through the arc gas discharge hole; a shooter seated on the first case and configured to drive the trip bar while moving through the arc gas discharged through the arc gas discharge hole; and a second case connected to cover the first case.