A heat exchanger 10 comprising first cells that cause a first fluid to flow therethrough, second cells that cause a second fluid to flow therethrough, and partitioning walls 12 that partition the first cells and the second cells. The partitioning walls 12 comprise: skeleton sections 12a having silicon carbide as the main component thereof; and filled sections 12b that comprise metal filled between the gaps of the skeleton sections 12a and covering the surface of the skeleton sections 12a. The partitioning walls 12 have a surface roughness Ra of at least 1.0 µm.