PURPOSE: To adhere a small metallic piece and a dielectric piece tightly, and to make a fine adjustment in a high frequency band by treating the surface of the dielectric substrate of an MIC circuit chemically.

CONSTITUTION: A conductor pattern 2 on the dielectric substrate 1 which uses, for example, "Teflon" as substrate material is formed by an etching treatment as to a parallel couple type filter, and then the surface 4 of the substrate 1 is treated chemially by sodium etching to realize an MIC circuit. The bottom is a grounding conductor 3. The MIC circuit allows a metallic piece and a dielectric piece to be adhered tightly and easily to the surface because the surface of the substrate 1 is treated by the sodium etching. Therefore, when an adjusting piece is adhered, it is fixed easily even if it is small, so a fine adjustment is made and the circuit is used stably even in a higher frequency band.