A tank type vacuum circuit breaker uses a columnar or cylindrical insulation rod at a connection portion between an operating mechanism unit and a vacuum valve. The insulation rod is connected to the operating mechanism unit and the vacuum valve by rod-shaped pins. To prevent the insulation rod itself from falling, connection is made by shifting phases of the pins 90 degrees, respectively, each pin being connected to the operating mechanism unit and the vacuum valve. Accordingly, the falling of the insulation rod, the use of an insulation support tube and an insulation support for ensuring mechanical strength, are avoided. Further fastening of those supports by bolts or the like is not needed. Increases in the number of components, the size of the shape of assembly members around the insulation rod, and weight due to such increases, are prevented.