To improve heat radiating characteristic of a heat generating element while an impedance between wiring and substrate is kept high without narrowing the wiring width and while an impedance between an element and metal substrate is kept high not to give any influence on the value of a high frequency element.

Insulation layers 3 (3a, 3b) are provided on a metal substrate 2 and a high frequency circuit is assembled on such insulation layers 3. An element generating heat in a high frequency circuit causes an insulation film 3 provided between the heat generating portion and metal substrate 2 to be formed as a thin film. The insulation film 3 provided between a high frequency route 4a or high frequency element and a metal substrate 2 should have the thickness which results in the desired impedance characteristic.