A method of manufacturing a cooling unit that includes a cooling plate in which a cooling fluid flows, the cooling plate having a structure in which a pair of tabular members are arranged to be opposed to each other with a cooling pipe, through which the cooling fluid flows, sandwiched between the tabular members, the manufacturing method includes: forming grooves for housing the cooling pipe in respective opposed surfaces of the pair of tabular members; forming projections projecting to inner sides of the grooves by applying an external force or joining a predetermined member to the respective opposed surfaces of the pair of tabular members; and combining each of the pair of tabular members and the cooling pipe by housing the cooling pipe in the grooves and expanding a diameter of the cooling pipe.