PURPOSE: To prevent loading miss of a filter by employing a mask blocking light of predetermined wavelength in exposure process thereby eliminating the need for a special filter at the time of exposure.

CONSTITUTION: A ceramic multilayer board 8, where conductor patterns 11, 11,... are connected through VIAS 12, is obtained by laminating a plurality of green sheets each formed with a circuit pattern and then baking the laminate. A conductor thin film 5 is then formed on the ceramic multilayer board 8 followed by formation of a resist film 6 on the sputter film 5. The resist film 6 is formed by applying a photosensitive resist on the sputter film 5, mounting a mask thereon, exposing the photosensitive resist with a light of specific wavelength, and then developing the resist. The ceramic multilayer board 8 formed with the resist film 6 is then plated and the resist is exfoliated thus forming a desired conductor circuit on the sputter film 5. The exposed sputter film 5 is then etched to form a single layer of a thin film circuit.