To provide a cooling device in which the temperature of cooling liquid is prevented from excessively decreasing when oil discharged from an oil pump is cooled by cooling liquid.

The cooling device has: a first oil reservoir 3 in which oil is reserved; an oil pump 2 for sucking/discharging the oil of the first oil reservoir 3; and an oil cooler 19 for cooling the oil by transmitting the heat of oil discharged from the oil pump 2 to the cooling liquid. A jet pump 11 is provided on a passage through which the discharged oil of the oil pump 2 is introduced to the oil cooler, the jet pump having: a first oil passage 12 through which the discharged oil of the oil pump 2 passes; a second oil passage 16 in which the oil of the first oil passage 12 passes through a jetting hole 15 and is ejected with a high pressure; and an auxiliary oil passage 13 connected to the second oil passage 16, through which the oil sucked to the second oil passage from the first oil reservoir 3 by a pressure difference from the second oil passage 16 passes.