Abstract: An analytical instrument includes an instrument body having a multiple external-device interfaces for connection with external devices, and a housing that covers the instrument body. The housing includes a housing panel having a first opening exposing the external-device interfaces and a plug structure having a first plug and a second plug. The first plug rotatably fits into the first opening and includes a second opening that exposes one of the external-device interfaces. The second plug is smaller than the first plug and is removably fitted into the second opening to close the second opening when no external device is connected to any of the external-device interfaces. When an external device is to connect to one of the external-device interfaces, the second plug is removed from the second opening and the first plug is rotated to expose the intended one of the external-device interface through the second opening.