A heat exchanger includes a heat exchanger body having a plurality of layer portions each having a plurality of flow paths, and having a configuration in which adjacent layer portions are joined to each other, an inflow header being configured that a fluid is introduced into the inflow header to flow into the plurality of flow paths, an outflow header being configured that a fluid flowing through the plurality of flow paths merges, a cover portion covering all joint portions of the adjacent layer portions or all joint portions of components of layer portions, the joint portions exposed on an outer surface of the heat exchanger body at a portion other than a portion where the inflow header and the outflow header are disposed, and a lead-out portion connected to the cover portion and forming an internal flow path communicating with a space between the cover portion and the heat exchanger body. The lead-out portion is configured to emit a fluid to a predetermined region set in advance.