A dielectric element assembly includes a plurality of dielectric layers stacked on each other in a direction of lamination and extends in an x-axis direction. A signal line is provided in the dielectric element assembly and extends in the x-axis direction. A reference ground conductor is provided on a positive side in a z-axis direction relative to the signal line. An auxiliary ground conductor is provided on a negative side in the z-axis direction relative to the signal line. Via-hole conductors connect the reference ground conductor and the auxiliary ground conductor and are provided in the dielectric element assembly on the negative side relative to the center in a y-axis direction. A portion of the signal line in a section which includes the via-hole conductors is positioned on the positive side in the y-axis direction relative to another portion of the signal line in a section which does not include the via-hole conductors.