Flexible circuit board and display device

A flexible circuit board, comprising:

• a substrate layer, comprising a first pad region, a second pad region, and a transmission line region between the first pad region and the second pad region;
• and
• a first conductive layer, at a first side of the substrate layer and comprising a first pad structure, a second pad structure, and a plurality of signal transmission lines extending along a first direction, wherein the first pad structure is in the first pad region, the second pad structure is in the second pad region, the plurality of signal transmission lines are in the transmission line region, and the transmission line region comprises a first single-layer region and a first double-layer region arranged along the first direction;
• in the first single-layer region, the first side of the substrate layer is provided with the first conductive layer, and a second side of the substrate layer is not provided with a conductive structure, in the first double-layer region, the first side of the substrate layer is provided with the first conductive layer, and the second side of the substrate layer is provided with a second conductive layer, the second side and the first side are opposite sides of the substrate layer.