A cooling structure is provided which includes: an evaporation chamber defined by a base plate having a boiling surface, a ceiling plate and a side wall; a plurality of plate-shaped fins arranged in parallel on the boiling surface, defining a plurality of coolant passages in the evaporation chamber, a liquid phase coolant flows through the coolant passages in one direction from one end portion thereof toward another end portion; a liquid return port formed in the side wall facing the one end portion of coolant passages; and a vapor port formed in the ceiling plate facing the other end portion of coolant passages, wherein space is formed between the ceiling plate and an upper end portion of the plurality of plate-shaped fins, the space expanding gradually from a liquid return port side of the side wall toward the vapor port.