An electronic device has a first circuit board, a first fan, a second circuit board, a first heat sink, and a first air ventilation duct. The first fan and the first circuit board are electrically connected together. The second circuit board is electrically connected to the first circuit board; the first heat sink is electrically connected to the second circuit board; and the first air ventilation duct is connected to the first fan and the first heat sink. The first heat sink introduce the heat generated by the electronic element on the second circuit board to the first fan for better cooling performance. Therefore, the present invention requires only the first fan and the second fan, but is able to provide high cooling efficiencies with a low noise signature.