The invention discloses a muffler device and a manufacturing method for a muffler. One shell out of an outer layer shell (21) and an inner layer shell (22) has a processed part (21a) that is processed into a shape protruding towards the other shell. An intermediate sheet (50) includes a receiving part (51) in a region that faces the processed part, and the receiving part (51) is formed into a shape that allows the processed part to enter the receiving part. Since the receiving part is formed in the intermediate sheet in a region that faces the processed part, the receiving part is positioned around the processed part when the processed part enters the receiving part, thereby preventing the receiving part from shifting with respect to the processed part.