Provided is a vacuum circuit breaker whose insulation cylinder contained in a gas-insulated-switchgear housing contains a vacuum valve and which can be downsized while the cylinder's required mechanical strength is retained, and a gas-insulated switchgear using the same is also provided. The vacuum circuit breaker includes a plurality of insulation cases that are arranged parallel to each other in a container filled with an insulating gas, and each of the plurality of insulation cases includes a first insulation frame in which a section orthogonal to its longitudinal direction is in a substantial square-bracket shape, a second insulation frame in which a section orthogonal to its longitudinal direction is in a substantial square-bracket shape and which is arranged with a gap from the first insulation frame in a manner that open sides of the substantially square-bracket shaped frames oppose to each other, and a vacuum valve that contains attachable and detachable electrodes and is housed in each of the plurality of insulation cases.