A power-supply wiring device, which protects electric wires between a sliding and fixed structures, and absorbs wire length change by sliding motion of the sliding structure, and a harness layout structure with the power-supply wiring device are provided. The power-supply wiring device includes a first case 5 for receiving a wire harness 4 folded into a U-shape, a moving portion 7, a harness holding member 8 disposed rotatably at the moving portion 7, a second case 44 receiving the harness holding member 8 freely to be swung. In the harness layout structure, the first case 5 and the second case 44 are mounted respectively on the sliding structure and the fixed structure, and the harness holding member 8 connects between the fixed and sliding structures.