A cooling unit includes a tank having an inlet port and a discharge port for refrigerant, first and second radiators connected to the tank, the first and second radiators each having a flow path, an inlet chamber defined in the tank for supplying the refrigerant flowing therein from the inlet port to the first radiator, a discharge chamber defined in the tank for discharging the refrigerant cooled in the second radiator to the discharge port, and a reservoir in which bubbles generated in the refrigerant are collected, the reservoir being provided between the inlet chamber and the discharge chamber in the tank.