A recessed portion is formed in a predetermined position in a heat-spreading component. A thermoplastic resin serving as a thermal interface material (TIM) is stored in the recessed portion. Meanwhile, a large number of filamentous thermo-conductive elements serving as the TIM are arranged to stand side by side on a surface of the heat-spreading component in which the recessed portion is formed (or on an exposed surface of an electronic component). Then, the heat-spreading component is fixed onto a board in such a manner that the surface of the heat-spreading component in which the recessed portion is formed faces the board and that a clearance is adjusted between the electronic component and the heat-spreading component. Thereafter, the resin is heated to a softening point thereof into a fluidized state, and the resin is flowed and filled into the clearance between the electronic component and the heat-spreading component.