A cooling unit includes a structure in which a box body made of resin and a plate lid made of metal are bonded together, in which at least one of an upper surface and a lower surface of the box body has an opening and the plate lid is bonded with the box body so as to block the opening, a wall surface of the box body is provided with a refrigerant inlet and a refrigerant outlet for allowing a refrigerant to flow in the box body, a flow path-forming rib is provided in the box body, and a part or an entirety of the box body is formed of a fiber-reinforced resin and/or a resin containing an inorganic particle filler.