To externally radiate heat efficiently by mounting an internal metal cover on an inside surface of an external metal cover, accommodating a dielectric multi-layered substrate within the inner metal cover, and making, in the internal metal cover, windows for interconnection between a high-frequency integrated circuit provided outside thereof and the dielectric multi-layered substrate provided inside thereof.

An internal metal cover 6 has a high-frequency integrated circuit 2 mounted on its upper surface and nearly in its central part 6c. The internal metal cover 6 is provided with through windows 6a and 6b in its both side projections 6d and 6e. The high-frequency integrated circuit 2, together with connecting wires and the windows 6a and 6b, is covered with synthetic resin all over its surface and set to form a covering 3. The internal metal cover 6 having a dielectric multi-layered substrate 1 accommodated therein and the high-frequency integrated circuit 2 are provided inside of an external metal cover 7. The external cover 7, which has a box shape, is tightly contacted at its inner lower side face 7c with an outer side surface 6f of the internal metal cover 6.