To provide a radiation device and an assembling method of the same, that can improve a heat transfer effect between heat pipes adjacent to each other.

This method includes a step (A) for providing a heat transfer base and the plurality of heat pipes. The heat transfer base has a plurality of grooves in which the heat pipes are press-fitted. Further, this method includes a step (B) for press-fitting the heat pipes into the grooves, and a step (C) for deforming adjacent parts of the heat pipes adjacent to each other, so that the heat pipes are kept into contact with each other. Thus, the heat transfer effect among the heat pipes can be improved.