A gas circuit breaker comprising: a pair of arc electrode (35a, 35b) disposed facing each other in a sealed container filled with an arc-extinguishing gas, the arc electrodes being capable of electrically flowing a current, an arc discharge being produced between both the electrodes at a time of current breaking action; a pressure increaser increasing a pressure of the arc-extinguishing gas to produce a pressure-increased gas in order to blow the arc-extinguishing gas to the arc discharge; an accumulating space reserving the pressure-increased gas; an insulation nozzle delivering the pressure-increased gas toward the arc discharge from the accumulating space; a switch causing the accumulating space to be in a closed state or a released state; and a trigger electrode disposed between the arc electrodes so as to be freely movable therebetween, and producing the arc discharge together with a movement, wherein the switch comprises a gap between the arc electrode and the trigger electrode, a gap between the insulation nozzle and the trigger electrode, or both of the gaps; the pressure-increased gas is blown to the arc discharge from a surrounding of the arc discharge to a center thereof; the pressure increaser comprises a cylinder and a piston, at least either one of the cylinder and the piston moves to compress the arc-extinguishing gas in the cylinder, thereby producing the pressure-increased gas; and a pressure of a heat exhaust gas produced from the arc discharge is prevented from acting as a compression repulsion force to the arc-extinguishing gas by the piston or the cylinder, characterized in that the gas circuit breaker further comprises a heat exhaust gas reserving space to temporarily reserve the heat exhaust gas produced from the arc discharge, wherein a pressure in the heat exhaust gas reserving space is caused to act as assist force to the compression of the arc-extinguishing gas by the piston or the cylinder. a pair of arc electrode (35a, 35b) disposed facing each other in a sealed container filled with an arc-extinguishing gas, the arc electrodes being capable of electrically flowing a current, an arc discharge being produced between both the electrodes at a time of current breaking action; a pressure increaser increasing a pressure of the arc-extinguishing gas to produce a pressure-increased gas in order to blow the arc-extinguishing gas to the arc discharge; an accumulating space reserving the pressure-increased gas; an insulation nozzle delivering the pressure-increased gas toward the arc discharge from the accumulating space; a switch causing the accumulating space to be in a closed state or a released state; and a trigger electrode disposed between the arc electrodes so as to be freely movable therebetween, and producing the arc discharge together with a movement, wherein the switch comprises a gap between the arc electrode and the trigger electrode, a gap between the insulation nozzle and the trigger electrode, or both of the gaps; the pressure-increased gas is blown to the arc discharge from a surrounding of the arc discharge to a center thereof; the pressure increaser comprises a cylinder and a piston, at least either one of the cylinder and the piston moves to compress the arc-extinguishing gas in the cylinder, thereby producing the pressure-increased gas; and a pressure of a heat exhaust gas produced from the arc discharge is prevented from acting as a compression repulsion force to the arc-extinguishing gas by the piston or the cylinder, characterized in that the gas circuit breaker further comprises a heat exhaust gas reserving space to temporarily reserve the heat exhaust gas produced from the arc discharge, wherein a pressure in the heat exhaust gas reserving space is caused to act as assist force to the compression of the arc-extinguishing gas by the piston or the cylinder.