A circuit board is a circuit board on which a predetermined circuit unit that causes heat and electromagnetic noise is disposed, and which is to be fixed to a conductive housing with a conductive screw. The circuit board includes: an insulator layer including an insulating plate-shaped base material; a conductor layer having a circuit pattern including a ground portion, which is disposed on at least one surface of the insulator layer; and a screw insertion hole that penetrates the insulator layer and the ground portion, and through which the conductive screw is to be inserted. The ground portion has a slit disposed between the screw insertion hole and the predetermined circuit unit. The ground portion has a ground bridge that electrically connects a portion of the ground portion between the slit and the screw insertion hole and a portion of the ground portion between the slit and the predetermined circuit unit.