To directly mount an organic thin film EL element on a printed wiring board by making a connecting position of two electrodes of an organic thin film EL element correspond to two through holes of the printed wiring board, and solidifying it by injecting a hardening agent after conductive paste is filled in these through holes.

Electrodes 12 and 14 exposed to the one surface side of an organic thin film EL element 10 and one surface of a printed wiring board 20 having through holes 21 and 22 arranged in a connecting position with these electrodes 12 and 14, are opposed to each other. Conductive paste 1 containing a binder using resin hardened by a hardening agent as a main agent and a conductive material, is injected from the other surface side of the printed wiring board 20, and is filled in the through holes 21 and 22, and is solidified by injecting the hardening agent.