An ebullient cooling device includes: an internal combustion engine cooled by boiling a coolant flowing through a coolant passage formed within the internal combustion engine; a gas-liquid separator that separates a coolant discharged from the internal combustion engine into a liquid-phase coolant and a gas-phase coolant; a condenser that is disposed on a downstream side of the expander, and cools the gas-phase coolant having passed through the expander so as to be changed into a liquid-phase coolant; a first passage that supplies the liquid-phase coolant from the condenser to the coolant passage formed within the internal combustion engine; a second passage that is branched from the first passage, and is connected to the gas-liquid separator; and a control valve that controls a supply state of a liquid-phase coolant supplied to the gas-liquid separator from the condenser through the second passage.