Circuit board cabinet

There is provided a circuit board cabinet which is capable of more reliably preventing flames of a fire in a shelf from spreading to external devices, without degrading cooling capability thereof. Flames of the fire occurring in the shelf rise within a slot, pass through a shield plate, and then enter a heat shield unit. In the heat shield unit, the flames are first blocked by a heat shield plate and substantially reduced in force while passing through holes formed through the heat shield plate. Portions of the flames which were not blocked by the heat shield plate reach a top board of the unit after passing through the holes, where they are reduced. Since there is a predetermined distance between the heat shield plate and the top board, the flames having passed through the heat shield plate spread horizontally to some extent and then reach the top board. Therefore, it is possible to reduce the force of the flames sufficiently by the top board. The flow of cooling air in normal use is sufficiently slower than that of flames, so that there is no fear of the existence of the heat shield unit causing a degraded heat dissipation.