A liquid cooling apparatus for use in a disk array apparatus which contains a plural number of units having a disk drive inside of a housing and disposed within a rack, including an air-blow fan, a pump for transmitting liquid coolant, a radiator for transmitting heat absorbed into the liquid coolant into outside air, and pipes for connection of the pump and radiator. The liquid cooling apparatus further includes a temperature sensor disposed at a position for detecting temperature of the liquid coolant, which temperature changes in response to electric power consumed within the plural number of disk drives, and a rotation speed of the pump is controlled in dependence upon a detection signal from the temperature sensor.