A liquid-cooled heat radiator 1 includes a heat radiation base 2 having a cooling-liquid channel 5, and an expansion tank 7 provided on the heat radiation base 2. The expansion tank 7 has a tank body 26 having an expanded portion 27, which expands upward and opens downward, and a bottom plate 28 joined to the lower end of the tank body 26 to thereby close a bottom opening of the expanded portion 27. A through-hole 29 is formed in the top wall of the expanded portion 27 of the tank body 26 and serves as a communication section for establishing communication between the interior and the exterior of the cooling-liquid channel 5. A hydrogen-permeable member 31 is fixedly fitted into the through-hole 29 so as to stop the through-hole 29. The hydrogen-permeable member 31 satisfies the relation B≧50 A, where A and B are water-vapor permeability and hydrogen permeability, respectively, of the hydrogen-permeable member 31. The hydrogen-permeable member 31 is formed from a single material selected from the group consisting of ethylene-propylene rubber, butyl rubber, fluorine-containing rubber, nitrile-butadiene rubber, and silicone rubber. The liquid-cooled heat radiator 1 can be free from an increase in pressure in the cooling-liquid channel 5.