A signal line and a circuit board that can be easily bent in a U shape and prevent unwanted emission include a line portion includes a plurality of laminated line portion sheets made of a flexible material. Signal lines extend within the line portion in an x-axis direction. Ground lines are provided within the line portion on a positive direction side in a z-axis direction with respect to the signal lines and have line widths equal to or smaller than the line widths of the signal lines. Ground lines are provided within the line portion on a negative direction side in the z-axis direction with respect to the signal lines. The signal lines overlap the ground lines when seen in a planar view from the z-axis direction.