Dielectric waveguide comprising a circular input/output electrode on its bottom surface and surrounded by an exposed dielectric portion thereof around which a conductor film is disposed. A short stub crosses through the exposed dielectric portion to couple the electrode and film together. The printed circuit board has a front surface formed with a generally-circular island-shaped electrode surrounded by a front surface-side ground pattern in a spaced-apart relation thereto, and a back surface formed with a strip line surrounded by a back surface-side ground pattern in spaced-apart relation thereto. An approximate center of the island-shaped electrode and one end of the strip line are coupled together, and the front surface-side ground pattern and the back surface-side pattern are coupled together. The input/output electrode of the dielectric waveguide and the island-shaped electrode of the printed circuit board are coupled together.