Abstract: A liquid cooling jacket (J1) transmits heat generated by a CPU (101) which is installed at a predetermined position to coolant supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket. The liquid cooling jacket includes a first flow passage (A1) on a side of the heat transmission fluid supply means, a second flow passage group (B1) including a plurality of second flow passages (B1a) branched from the first flow passage (A1), and a third flow passage (C1) installed at downstream side of the plurality of the second flow passages (B1a), and collecting the plurality of the second flow passages (B1a), wherein the CPU (101) mainly dissipates the heat to the second flow passage group (B1).