PURPOSE: To eliminate the need for a chip capacitor for DC interruption by providing a strip line being a component of a required filter to the input/output circuit board having the strip line.

CONSTITUTION: A half wavelength coupling filter is formed by opposing coupling lines 2a, 2b whose length is respectively a half wavelength λ/4 to each other and placed at the tip of strip lines 1a, 1b on the front side of a ceramic board 3 whose rear side is provided with a conductive layer 4. When the two boards 3 are employed and connected to a semiconductor chip 5 as an external circuit, a chip capacitor for DC interruption is not required and production of short- circuit due to flowing of solder or paste at joining of the chip capacitor is prevented.