Abstract: An enclosed switchboard has a contact frame fitted with contacts which can move relative to a unit frame having a circuit breaker, an electromagnetic switch, and an auxiliary relay, etc. mounted thereon. The contacts can be operated to disconnected, test, and connected positions with the unit frame disposed in the panel frame by an operating lever inserted into a window on a closed door covering the front side of the panel frame. A shutter mechanism is provided between the window and the insertion position of the operating lever in order to cover the insertion position of the operating lever for preventing insertion of the operating lever when the operating handle is set to an ON position, and an interlocking mechanism is also provided between the shutter mechanism and the operating handle of a circuit breaker disposed at the unit frame.