A structure of flexible printed circuit boards comprising: a rectangular substrate; a total of four flexible printed circuit boards, the four flexible printed circuit boards being bar-type flexible printed circuit boards, each positioned along an entirety of a respective edge of the substrate, wherein each bar-type flexible printed circuit board has a first rectangular anode pad and a first rectangular cathode pad , positioned on the end portion of one side of the bar-type flexible printed circuit board, that are mounted in parallel to each other in a length direction of the bar-type flexible printed circuit board, and also has a second rectangular anode pad and a second rectangular cathode pad , positioned on the opposing end portion of the same side of the bar-type flexible printed circuit board in the length direction of the bar-type flexible printed circuit board, that are mounted in parallel to each other in a direction that is perpendicular to the length direction of the flexible printed circuit board; and four pairs of soldering portions or four pairs of wire bonding portions , each of which respectively connects a first rectangular anode pad and a first rectangular cathode pad of one of the four bar-type flexible printed circuit boards to a second rectangular anode pad and a second rectangular cathode pad mounted on a neighboring end portion of another of the four bar-type flexible printed circuit boards and extending in the same direction as the first rectangular anode pad and the first rectangular cathode pad , making the first rectangular anode pad and the first rectangular cathode pad conduct electricity with the second rectangular anode pad and the second rectangular cathode pad . a rectangular substrate; a total of four flexible printed circuit boards, the four flexible printed circuit boards being bar-type flexible printed circuit boards, each positioned along an entirety of a respective edge of the substrate, wherein each bar-type flexible printed circuit board has a first rectangular anode pad and a first rectangular cathode pad , positioned on the end portion of one side of the bar-type flexible printed circuit board, that are mounted in parallel to each other in a length direction of the bar-type flexible printed circuit board, and also has a second rectangular anode pad and a second rectangular cathode pad , positioned on the opposing end portion of the same side of the bar-type flexible printed circuit board in the length direction of the bar-type flexible printed circuit board, that are mounted in parallel to each other in a direction that is perpendicular to the length direction of the flexible printed circuit board; and four pairs of soldering portions or four pairs of wire bonding portions , each of which respectively connects a first rectangular anode pad and a first rectangular cathode pad of one of the four bar-type flexible printed circuit boards to a second rectangular anode pad and a second rectangular cathode pad mounted on a neighboring end portion of another of the four bar-type flexible printed circuit boards and extending in the same direction as the first rectangular anode pad and the first rectangular cathode pad , making the first rectangular anode pad and the first rectangular cathode pad conduct electricity with the second rectangular anode pad and the second rectangular cathode pad . <EOS>