Cooling jacket

A cooling jacket for cooling a heat-generating element through transmitting heat-generation into a coolant flowing within an inside of the cooling jacket, which is mounted within an electronic apparatus, and includes a base portion, and a cover portion. The base portion includes a heat-transfer surface in proximity to a surface of the heat-generating element, and a plurality of wall portions. Each wall portion is defined to extend into a direction perpendicular to the heat-transfer surface, thereby defining flow passages for the fluid coolant between the wall portions. The cover portion is attached on the base portion surrounding a periphery of the base portion, thereby defining a passage for guiding the fluid coolant into the base portion. The base portion builds up the sector-shaped flow passages and a summit portion at a central portion of the base, and has a configuration that is thermally isotropic to the heat-generating element.