A cooling
system applying a thermo
siphon therein, being superior in energy saving and / or
ecology, with an effective cooling, and also an electronic apparatus applying that therein, in particular, for cooling a CPU 200 mounted on a
printed circuit board 100 within a housing thereof, comprises a heat-receiving jacket 310, being thermally connected with a surface of the CPU generating heats therein, and for evaporating liquid
refrigerant stored in a pressure-reduced inner space with
heat generation thereof, a condenser 320 for receiving
refrigerant vapor from the heat-receiving jacket within a pressure-reduced inner space thereof and for condensing the
refrigerant vapor into a liquid by transferring the heats into an outside of the apparatus, a vapor tube 331, and a liquid return tube 332, with applying the thermo
siphon for circulating the refrigerant due to
phase change thereof, wherein the condenser forms fine grooves on an inner wall surface thereof along a direction of flow of the refrigerant, and is also formed flat in a cross-section thereof, for cooling the refrigerant vapor from the heat-receiving jacket on the inner wall surface thereof, efficiently.