To provide a cooling body, in which a liquid coolant flows once through the interior, heightening the cooling capability without any increase in flow of the liquid coolant.

In the cooling body coming into contact with a heating unit and provided with a once-through passage disposed in the interior for the liquid coolant to flow once through a zigzag once-through passage allowing the liquid coolant to flow from one end to the other end while the flow direction is changed to the direction vertical to the contact surface and to the parallel direction so as to come into contact with both surfaces alternately is provided between both opposite surfaces which are contact surfaces between the cooling body and the heating unit.