A high power circuit breaker using sulfur hexafluoride as an interrupting medium has a main movable sleeve contact which surrounds an axially movable interrupter contact. The interrupter contact further serves as a valve between high pressure and low pressure SF6 filled regions to permit gas blast through the separating interrupting contacts when the valve is opened. The main movable contact has an extension serving as a downstream shutoff valve which pre-encloses a volume downstream of the interrupter contact prior to the opening of the contacts. The interrupter contact is provided with an extending flange which serves as a short-circuited turn which cooperates with an energizing coil. Energization of the coil repels the shortcircuited turn defined by the flange to initially open the blast valve. High-pressure gas is then applied against the movable contact to move the interrupter contact fully open after the valve is opened. The contacts are synchronously operated so that the contacts open immediately prior to a current zero. The opened contacts are disposed in the high-pressure SF6 region.