A cooling device comprises a circulation passage through which a liquid coolant flows, and a pump provided in the circulation passage configured to circulate the liquid coolant along the circulation passage. The pump includes, (1) a pump casing including a pump chamber into which the liquid coolant flows, (2) an impeller mounted in the pump chamber to push out the liquid coolant from the pump chamber to the circulation passage, and (3) an injection portion provided in the pump casing configured to inject the liquid coolant to the pump chamber.