To provide a receptacle, a plug, and a wiring device which are in conformity with the IEC standard, and in which signal transmission wiring is facilitated.

The plug 1A is equipped with a fitting part 12 in which a round hole-shaped fitting hole 13 is opened, pin terminals 15a, 15b for a voltage electrode arranged and installed inside the fitting hole 13 along the plug insertion/extraction direction, and pin terminals 16a, 16b for signal transmission arranged and installed at the outside site of the fitting hole 13 along the plug insertion/extraction direction. The receptacle 2A is equipped with a power supply terminal connecting part 3Ab in conformity with the IEC standard to which the pin terminals 15a, 15b for the voltage electrode attached to the plug 1A are insertably and extractably connected, and a signal terminal connecting part 3B which is installed at the site different from that at the power supply terminal connecting part 3A, and to which the pin terminals 16a, 16b for the signal transmission attached to the plug 1A are insertably and extractably connected.