A cooling device includes a heat sink base plate for mounting on a circuit board to absorb waste heat from a heat source, a radiation fin unit consisting of a set of radiation fins, mounted on the heat sink base plate opposite to the circuit board and defining a plurality of heat-dissipation passages between each two adjacent ones of the radiation fins, a cooling fan unit mounted on the radiation fin unit for creating currents of air toward the heat-dissipation passages, a plurality of thermal tubes supported on the heat sink base plate and fastened to the radiation fins. Each radiation fin has first wind guiding wall portions and second wind guiding wall portions respectively tilted in reversed directions to facilitate the flow of air through the heat-dissipation passages.