PURPOSE: To achieve high voltage and compactness of a circuit-breaking part and obtain a gas-blast circuit-breaker having a stable circuit-breaking ability by shutting an open part from the periphery of the apart position of a stator and a mover to the position at only an initial period of shutting operation.
CONSTITUTION: The tip of a gas-discharging guide 12 is moved toward a mover side, and an open part formed in the side plane of a cylinder 11 is opened in the section from the position at an on state to the periphery of pole open position of a mover 4 and a stator 3. Even if the open part 10 is opened during the period of moving to the periphery of pole open position in circuit-breaking operation, gas flow from a hollow nozzle 6 of the mover is scarcely caused. That is, since there is no vain gas flow which lowers the circuit-breaking ability, the length L between poles can be increased without causing bad effects on the circuit-breaking ability. In this way, high voltage of the circuit-breaking part is achieved and at the same time a gas-blast circuit-breaker with stable circuit-breaking ability is obtained.