An electrical circuit breaker in which a pressurized gas such as SF6 operating on a closed gas circuit is utilized to extinguish the arc drawn between the switching contacts and perhaps also to actuate the contacts themselves includes an upstanding hollow insulator column at the top of which is supported a switch contact chamber and an adjacently located readiness tank containing the pressurized gas ready for delivery to the contact chamber as soon as a switching-out sequence is initiated. To assure rapid replenishment of the gas in the readiness tank so that a second switching-out operation can take place immediately, and at the same gas pressure as the first one should this be necessary, for example, due to the persistence of a short circuit on the line to which the breaker is connected, replenishment gas is stored in a cylinder at the lower end of the insulator column and this cylinder contains a piston which is driven in a direction to expell the gas stored in the cylinder and deliver it to the readiness tank through an interconnecting pipe line as soon as the gas pressure drops in the readiness tank as a result of delivery of the pressurized gas from the latter into the switch contact chamber. Thus the drop in gas pressure in the readiness tank resulting from the first disconnection of the switching contacts is compensated for and restored immediately by the re-pressurizing action resulting from the displacement of the piston.