A cooling device for cooling a heat-generating component includes a circulating passage arranged to have coolant circulate therein, a centrifugal pump including a first case made of metallic material, a second case made of resin material, and an impeller accommodated in the pump chamber, and a radiator provided at the circulating passage and being operable to release heat from the coolant. The first case has a surface arranged to contact the heat-generating component. The second case forms a pump chamber between the first case and the second case. The pump chamber stores the coolant therein. The impeller includes open-type vanes arranged to pressurize the coolant as to have the coolant flow through the circulating passage. The cooling device has a high cooling efficiency as well as a high operating efficiency of the motor while having a simple construction and a small overall size and a small thickness.