Abstract: A vacuum circuit breaker comprises a base, a support frame and an insulating frame. The insulating frame has a plurality of housing portions juxtaposed and separated from one another. These housing portions are made of plastics as a unit. The insulating frame is supported by the support frame which is detachably mounted on the base. The vacuum circuit breaker has a plurality of vacuum valves each having a fixed and a movable electrode, and plural sets of main circuit conductors. Each vacuum valve and each set of the main circuit conductors are provided in each housing portion. The vacuum circuit breaker has a operating mechanism moving the movable electrode of the vacuum valve, and the operating mechanism is supported by the support frame.