To use a thick copper foil, without the use of a bonding agent by applying an insulation slurry to the surface of an insulation layer on which a conductor circuit is formed, for the conductor circuit to be buried, or by press-contacting in lamination the conductor circuit to the insulation layer in soft condition, for the conductor circuit to be buried in the insulation layer, for multiple layers.

On the surface of a transfer sheet 1 on which a conductor circuit 4 is formed, an insulating slurry 5 containing an organic resin is formed into a thickness corresponding to an insulation layer, while being thicker than the conductor circuit, and the insulating slurry 5 is dried or semi-cured. By pouring the slurry 5, the conductor circuit 4 is completely buried in the insulation layer 5, formed by drying of slurry without occurrence of voids. Thereby, degradation in electric characteristics is entirely eliminated without requiring use of a bonding agent.