Flat wiring structure

A flat wiring structure including a plurality of layers, the flat wiring structure comprising:

• a power supply layer;
• and
• a first ground layer and a second ground layer laminated with the power supply layer sandwiched between the first ground layer and the second ground layer, wherein
• in a plan view of the flat wiring structure when viewed from a direction along a lamination direction of the first ground layer, the power supply layer, and the second ground layer, the power supply layer has a width in a short direction smaller than those of the first ground layer and the second ground layer, and the power supply layer is provided at a position covered with the first ground layer and the second ground layer.