A liquid cooling system for use in an electronic apparatus, being super small-sized and thin in the shape and being suitable for cooling a heat-generation part, such as, a semiconductor element having large amount of heat generation, for example, with maintaining the corrosion resistance thereof for a long time period, comprises: a pump (1) for supplying a cooling liquid; a heat-receiving jacket (2), being supplied with the cooling liquid, for receiving heat from an electronic parts; a radiator, being supplied with the cooling liquid passing through the heat-receiving jacket, for radiation heat; and flow passages for circulating the cooling liquid in a route passing through the radiator back to said pump, wherein an ion exchange bag (9), having an ion exchange resin (11) and a bag enclosing it therein, is disposed in a part of the constituent parts of the liquid cooling system, and/or the ion exchange bag (9) is exchangeable.