To provide a small gas circuit breaker capable of effectively cooling a hot gas flow.

Arc contacts 3a, 4a are provided in a cylindrical tank 1 filled with arc-extinguishing gas 2 under a contact condition during a normal operation. During current interruption, arc generated between both contacts by a relative movement opening is blown to the arc-extinguishing gas 2 to be extinguished, so that a stationary side hot gas flow 11a generated in the arc-extinguishing is guided in a direction for separating from the stationary arc contact 3a by an exhaust cylinder 101 provided coaxially in the tank 1. The exhaust cylinder 101 comprises an inner cylinder 102 having an inner cylinder passage 102a inside, a cup-shaped outer cylinder 103 having an outer cylinder passage 103a between the outer cylinder 103 and the inner cylinder 102 and coaxially covering the inner cylinder, and a hole 106 formed on a wall of the inner cylinder 102 and communicating inside and outside. After the stationary side hot gas flow 11a flows in the inner cylinder passage 102a in a direction for separating from the stationary arc contact 3a, it returns and flows in the outer cylinder passage 103a in an opposite direction, and is exhausted from the exhaust cylinder 101.