A phase change evaporator includes multiple heat-dissipating fins formed on an evaporator body of the evaporator. A cooling device includes the evaporator, a condenser, a coolant output pipe and a coolant return pipe connected between the evaporator and the condenser, and coolant filled inside a closed coolant circulation loop formed by the evaporator, the condenser, the coolant output pipe and the coolant return pipe. When the evaporator body absorbs heat, the coolant inside the evaporator body is converted into a gaseous state by the heat and then quickly dissipates the heat absorbed thereby through the heat-dissipating fins for a part of the gaseous coolant to be condensed to resume heat absorption and for the remaining part to flow to the condenser through the coolant output pipe to be condensed to a liquid state and return to the evaporator body along the coolant return pipe for heat absorption.