A maintenance-free cooling structure is provided which, by removing bubbles produced on a boiling surface utilizing an action other than buoyancy, heat change (heat transfer) is effectively brought about on the boiling surface, thus enabling efficient cooling and its miniaturization and low power consumption. The cooling structure has an evaporation chamber 11 connected through a vapor pipe and a liquid return pipe to a condensation chamber to allow a phase change to occur from a vapor phase coolant V to a liquid phase coolant L. In the evaporation chamber, as a result of contact of the liquid phase coolant L with the boiling surface of a base plate 21 and/or with plate-shaped fins, the phase change occurs from liquid to vapor. The evaporation chamber has an aperture operating as a vapor port 25 for the vapor pipe which is formed in a neighboring position along an inner circumferential surface 23a of a cylindrical plate 23 in a ceiling surface 22a and an aperture operating as a liquid return port for the liquid return pipe which is formed in a position neighboring to an end edge along the boiling surface on an inner circumferential surface on a side opposite to the vapor port 25, so that the flow-in direction of the liquid phase coolant is in parallel to the boiling surface.