A circuit board includes a first section on a left side of a third section in a signal-conductor-layer left-right direction and extending in parallel or substantially in parallel with the third section in a signal-conductor-layer front-back direction when viewed in a stacking direction. The first section includes first thin line portions and first thick line portions, each of the first thick line portions has a line width greater than a line width of each of the first thin line portions. The first thin line portions and the first thick line portions are alternately arranged in the signal-conductor-layer front-back direction. In the signal-conductor-layer left-right direction, center lines of the first thin line portions are positioned leftward relative to center lines of the first thick line portions.