A gas circuit breaker includes a sealed container in which the arc-extinguishing gas is enclosed, a first fixed contactor portion and a second fixed contactor portion fixed to the sealed container, and a movable contactor portion which moves between the first fixed contactor portion and the second fixed contactor portion, to conduct and break current between them, in which an arc generated at a time of current breaking action is extinguished by spraying the arc-extinguishing gas, the gas circuit breaker includes a gas chamber configured to accumulate the unnecessary gas, the sealed container is formed by joining ends of the two hollow truncated cone portions, each having a large opening diameter, with the cylindrical portion therebetween, and the gas chamber is formed inside the cylindrical portion forming the sealed container.