A gas circuit breaker includes: a pair of electrodes provided so as to be able to come in contact with and separate from each other; and an insulating material that is placed so as to generate a decomposition gas in response to a direct or indirect action from an arc occurring between the pair of electrodes when a current is broken, wherein the decomposition gas generated from the insulating material when the current is broken is configured to be utilized for extinguishing the arc, and wherein an ablative material that does not include hydrogen atoms but has a carbon-oxygen bond in a main chain or ring part is used as the insulating material.