A circuit substrate includes: a plurality of signal wirings formed at different positions of the circuit substrate in a thickness direction and extending in parallel in the circuit substrate; and ground layers or power supply layers formed at both sides of the circuit substrate in the thickness direction by interposing the plurality of the signal wirings between the ground layers or between the power supply layers, wherein the plurality of signal wirings are electrically coupled with each other by a plurality of conductors formed at an interval narrower than an interval by which a resonance is caused.