Cooling jacket

A cooling jacket for cooling a heat-generating element 300 through transmitting heat-generation therein into a coolant flowing within an inside thereof, which is mounted within an electronic apparatus, comprises a base portion 110 , having a heat-transfer surface 111 to be contact on a surface of the heat-generating element, and a plural number of wall portions 113 , each being defined to extend into a direction perpendicular to the heat-transfer surface, thereby defining flow passages 114 for the liquid coolant between the wall portions; and a cover portion 120 , being attached on the base portion surrounding a periphery thereof, thereby defining a passage for guiding the liquid coolant into the base portion, wherein the base portion builds up the sector-like shaped flow passages and a summit portion at a central portion of the base, and has a configuration being thermally isotropic to the heat-generating element to be contact thereon.