Abstract: According to an embodiment, a cooling device for cooling a constituent element housed in a housing of a unit subjected to an influence of a generated magnetic field includes a water cooling mechanism and at least one air cooling mechanism. The water cooling mechanism cools the constituent element by cooling a cooling plate with a flow of water flowing through a pipe passing through the cooling plate arranged in the housing. The air cooling mechanism is arranged on an outgoing side where the flow of water flowing through the pipe is outgoing from the housing and cools the constituent element by discharging air in the housing along with the water flow in accordance with the water flow.