A basic unit portion configured by a standard unit and a variable unit portion whose shape is configured to be changeable. The basic unit portion includes: a first pressure tank with a first opening portion; a circuit breaker; a first bushing; a first disconnecting switch. The variable unit portion includes: a busbar; a second pressure tank with a second opening portion; a second bushing whose necessary number is disposed in accordance with the number of circuits to be externally connected; and second disconnecting switches which are arranged between the busbar and the second bushing. The first opening portion of the basic unit portion and the second opening portion of the variable unit portion are joined facing each other to form into a constitutional body.