In a flat circuit comprising a plurality of flexible conductors 27 and an insulating covering 28, there is formed a free end 25 which is elastically deformable in an engaging direction of connectors. A connector 24 adapted to be engaged with a connector 37 of an auxiliary component 26 is mounted on a conductor exposing part 32 in the free end 25. The flat circuit may be bent at a position of a desired length L so as to form the free end 25 at a side including an end edge 23.