A gas circuit breaker 1 includes an insulation nozzle 23 that guides arc-extinguishing gas to an arc between a first arc contactor 21 and a second arc contactor 41 when a trigger electrode 31 becomes an opened state relative to the first arc contactor 21. The second arc contactor 41 has an opening 41a for spraying the arc-extinguishing gas, and the opening 41a is closed by the trigger electrode 31 in the first half of a current breaking action, and is opened by separation of the trigger electrode in the latter half of the current breaking action. An opening area of a first exhaust port 41b formed between the second arc contactor 41 and the insulation nozzle 23 for exhausting the arc-extinguishing gas is 0.2 times or more and two times or less of an opening area of the opening 41a of the second arc contactor 41.