Different-pitch flat cable connection structure, pitch-conversion flat cable, and method for producing pitch-conversion flat cable

Provided is a different-pitch flat cable connection structure for connecting a first flat-cable part that includes a plurality of first conductors arranged in a stripe pattern with a first pitch to a second flat-cable part that includes a plurality of second conductors arranged in a stripe pattern with a second pitch smaller than the first pitch, and establishing electrical continuity between the first conductors and the second conductors. The different-pitch flat cable connection structure includes a connection sheet laminated on one surface side of ends of the first conductors and ends of the second conductors in which at least the one surface side of the ends is exposed. The connection sheet includes a base layer, a plurality of third conductors laminated on another surface side of the base layer so as to extend between the first conductors and the corresponding second conductors in a one-to-one relationship, and a plurality of conductive adhesive layers disposed between facing surfaces of the first conductors and the third conductors and between facing surfaces of the second conductors and the third conductors.