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.