(57) High-voltage circuit breaker of self-blasting type with a gas reservoir for arc extinction consisting of two parts, a pressure storage volume (6) and a puffer volume (7). The two volumes (6, 7) are separated by a wall (11) with a non-return valve (12,13,14) which is closed when the pressure in the pressure storage volume (6) is higher than in the puffer volume (7). During an opening operation, the gas in the puffer volume is compressed because the distance between the wall (11) and the puffer piston (16) then decreases. The invention improves the breaking capacity on the occurrence of a breaking operation immediately following an auto-reclosing by arranging the puffer piston (16) axially displaceable against the action of one or more springs (17). During the high-pressure phase in the first breaking operation the piston (16) is moved against the resistance of the springs 17 and, when the pressure drops towards the end of the movement, a gas puff is injected into the pressure storage volume under the force of the re-expanding springs 17. This results in a considerable reduction of the gas temperature in the pressure storage volume which in this way achieves in better condition for the next breaking operation.