A series unit comprises an input terminal and an output terminal each composed of a tubular receptacle having a center conductor and an external conductor provided concentrically with the center conductor, a television terminal, and a unit case for supporting the input terminal, the output terminal, and the television terminal. The external conductors of the terminals are electrically interconnected through the unit case. The center conductors are electrically interconnected in the space defined inside the unit case. The orientation of the connection end portion of the unit case is perpendicular to the connection/disconnection end portion to/from which the terminal of the cable is connected/disconnected. The input terminal and the output terminal are constituted as movable terminals rotatable at the connection end portions of the unit case. The planes defined by the center axes of the connection/disconnection end portions by the rotation of the movable terminals are perpendicular to each other.