A blade server including a cooling structure to be loaded with a CPU of high performance is provided. In order to enhance draining performance of a condensed working fluid which stays between fins, a vapor condensing pipe is used, in which grooves are formed in a direction substantially parallel direction with a pipe axis direction on the above described pipe inner surface, a section of a row of the above described fins is exposed on a side surface of the above described groove, the above described groove is disposed at a lower side in the vertical direction from the center line in the pipe axis direction of the vapor condensing pipe when the above described groove is installed in the above described vapor condensing pipe, and a wick with a wire space smaller than the fin space of the above described fin row is filled inside the above described groove.