An ebullient cooling device includes: a coolant passage configured to be formed inside an internal-combustion engine, and allow a coolant that cools the internal-combustion engine by boiling to flow therethrough; an expander configured to be driven by the coolant that has boiled in the internal-combustion engine; a condenser configured to be located at a downstream side of the expander, and cool the coolant that has passed through the expander; and a heat exchanger configured to cool a cooling object by heat exchange with the coolant, wherein a low-pressure region including the expander and the condenser and a high-pressure region other than the low-pressure region are formed in a path through which the coolant circulates, and a passage connecting to a part through which a liquid-phase coolant flows and a passage connecting to the low-pressure region are coupled to the heat exchanger.