A vehicular cooling device includes a heat medium circuit, a waste heat supply device, a heat exchanger, and a heater. A heat medium circulates in the heat medium circuit. The waste heat supply device is configured to generate a waste heat in accordance with operation of the waste heat supply device and supply the waste heat to the heat medium. The heat exchanger is configured to exchange heat between the heat medium and a lubricant lubricating a transmission of a vehicle. The heater is configured to heat the lubricant that is inside the heat exchanger. According to this vehicular cooling device, since the heater heats the lubricant, the transmission can be warmed up early, and thereby friction in the transmission decreases to improve fuel economy.