A circuit device includes a dielectric substrate including a first face and a second face opposite side of the first face; a coplanar line including a first line, a second line and ground electrodes, the first line and the second line being decupled mutually, the ground electrodes formed around the first line and the second line, the first line, the second line and the ground electrodes formed on the first face of the dielectric substrate; a capacitor for connecting the first line and the second line; a termination resistor connecting the second line; a microstrip line formed on the second face of the dielectric substrate; and a conducting portion formed in the dielectric substrate and electrically connecting the first line and the microstrip line.