Abstract: A dual wiring system which has improved easy exchangeability and function expandability of function unit, and is capable of constructing a higher-order system by controlling plural function units in a coordinated fashion. A plurality of base units are mounted in wall surfaces of a building structure, and connected to both of an electric power line and an information line installed in the building structure. A function unit is detachably connected to each of the base units, and provides at least one of functions for supplying electric power from the electric power line, outputting information from the information line, and inputting information into the information line. A control unit is detachably connected to the function unit or the base unit, and controls at least two of the function units connected to the electric power line and the information line through the base unit(s) in a coordinated fashion.