PURPOSE: To attain mutual connection of many IC boards, by bringing plural microwave IC boards into contact through a dielectric board therein, flowing a current via a ground conductor film, and eliminating improper contact between ground metallic conductors fixed to the boards.

CONSTITUTION: A board 13 for connection is inserted between dielectric boards 11, 12 mounting circuits. Microstrip lines 21, 22 forming the surface condutor of the boards are connected via metallic ribbons 41, 42 and a microstrip lines 23. Further, a current flowing at the back of the boards flows to the ground conductor film 33 through the metallic ground conductor 51 from the ground conductor film 31 at the back side of the boards. The improper contact between the metallic ground conductors 51, 52 fixed to the boards 11, 12 or an instable cause of the electric characteristic such as microwave resonance is eliminated, allowing to attain many connection of the IC boards mutually.