A plug housing for accommodating a plug for connecting to the adapter, includes a housing body having an inside surface, the inside surface forming a through hole accommodating the main body of the plug, a slope portion formed on the inside surface and configured to cause the main body of the plug to move forward by a reaction force received from a second lever formed on the side surface of the plug when the main body of the plug is accommodated in the through hole and the second lever is pushed down by the slope portion, and a restrict portion formed on the inside surface and configured to restrict the forward movement of the main body of the plug.