To provide a thin film circuit board exhibiting excellent adhesion between an organic insulation film provided on the surface of a substrate and a metallization (electrode material) arranged thereon, its producing method and a high performance high frequency module employing the thin film circuit board.

On the surface of an organic insulation film 2 formed on a substrate 1, a surface reforming layer having a surface reforming coefficient of 0.1-0.5 is provided and a metallization 5 (4) is applied to the surface of the organic insulation film 2 provided with the surface reforming layer in order to enhance adhesion strength of the metallization 5 (4). The surface reforming coefficient is the ratio of C forming a functional group to C existing on the surface of the organic insulation film and represented by formula (1). Surface reforming coefficient = total number of functional groups/total number of C existing on the surface of the organic insulation film...(1).