A circuit board, included in an inverter device that outputs AC current to a motor for driving a vehicle, includes: an insulation layer; a first conductor formed on a first side of the insulation layer, and upon which a semiconductor chip included in a lower arm of an inverter circuit is mounted; a second conductor formed on a second side of the insulation layer opposite to the first side thereof, and connected to a ground of the vehicle; and an inductor connected in parallel with a parasitic capacitance created between the first conductor and the second conductor, thus constituting a parallel resonator together with the parasitic capacitance.