Circuit board and printed board

A circuit board comprising:

• a printed board that includes an insulating base and a plurality of conductors disposed in layers in the insulating base;
• and
• an electronic component that is mounted on the printed board, wherein
• the plurality of conductors includes:
• at least one signal line electrically connected to the electronic component;
• and
• at least one potential fixed layer fixed to a predetermined potential and arranged to face the at least one signal line across at least a part of the insulating base in a thickness direction of the printed board,
• the at least one potential fixed layer has a facing surface facing the at least one signal line, and is provided with a high magnetic film on the facing surface,
• the at least one signal line includes a facing line that faces the high magnetic film across the at least the part of the insulating base in the thickness direction,
• the high magnetic film has a magnetic permeability higher than that of the at least one potential fixed layer, thereby increasing an impedance of the facing line, and
• the high magnetic film is disposed to overlap the facing line in the thickness direction.