In an electronic apparatus having a heat-generating element therein, a cooling jacket 100 for transmitting heat generated from the heat-generating element 200 into to a liquid coolant flowing therein, comprises: a cover 130 building up a heat transfer surface to be in contact with a surface of the heat-generating element; a passage 110 for the liquid coolant, which is formed neighboring with the heat transfer surface and wound round in a "S"-like manner within an inside of a main body 120 of the cooling jacket; and an inlet 111 and an outlet 112 attached at both ends of the flow passage of the liquid coolant, and further a dispersion member 150 is disposed in the flow passage, being built up by gathering a plural number of members, each of which has a "U"-like cross-section of an aspect ratio from 10 to 20, thereby diffusing the liquid coolant therein, so as to transfer the heat from the heat-generating element thereto with high efficiency, and thereby enabling to cool down the heat-generating element, fully, even with a relatively small amount or volume of the liquid coolant.