Abstract: A metal honeycomb substrate includes a tubular body, a flat plate, and a wavy plate. The tubular body has a receiving portion. The wavy plate is stacked with the flat plate to form a spiral structure received in the receiving portion. The wavy plate has a wavy-shaped cross section and includes a second region and a continuous region connected to the second region. The wavy-shaped cross section includes peak portions and valley portions. The wavy plate has a solder region overlapping at least one portion of at least one of the second region and the continuous region. Solders are on outer sides of the peak portions and outer sides of the valley portions which are in the solder region. A ratio of an area of the solder region to an area of the wavy plate is in a range between substantially 20% and substantially 66%.