To make useable plugs of two or more voltage specifications to be selectively used for one kind of outlet as appropriate without using an adaptor.

An outlet 1 includes a first plug blade receiving portion 2 to which an electric potential of 0 V is applied and multi-pole second plug blade receiving portions 3 to which different direct-current electric potentials are applied, respectively. The multi-pole second plug blade receiving portions 3 have different shapes or dispositions depending on suitable voltages applied thereto. One plug blade 11a of a plug 10 is connected to the first plug blade receiving portion 2. The other plug blade 11b of the plug 10 has a different shape or disposition corresponding to the different shape or disposition of the second plug blade receiving portions 3 so as to be connected to any single-pole second plug blade receiving portion 3 corresponding to the received suitable voltage out of the multi-pole second plug blade receiving portions 3.