A cooling fin unit includes a plurality of cooling fins and a heat guide pipe. Each of the cooling fins has a through hole at the main body thereof and the heat guide pipe passes through the through hole respectively. A recess part is provided to indent toward a side of the main body near the outer side of the through hole and the recess part has a receiving space communicating with the through hole. A heat conductive medium, which is received in the receiving space, is heated up to become a state of melting to fill with spots between the outer surface of the heat guide pipe and the respective through hole.