A plug connector is detachably matable with a cap connector. The plug connector includes a lever performing mating with and unmating from the cap connector. The lever includes a cam groove for receiving a first boss of the cap connector, a boss rotation hole for receiving a second boss of an outer housing of the plug connector, and a catching protrusion sliding hole for receiving a catching protrusion of an inner housing of the plug connector. A first turning operation of the lever during unmating from a fully mated state extracts an interlock busbar of the plug connector from the cap connector to remove a short circuit of first conducting wires of the cap connector. A second turning operation of the lever during unmating moves a releasing protrusion into a clip spring of the plug connector to open the clip spring.