To enable setting of the improvement in appearance of a vehicle and the output characteristics of an engine in accordance with a user's desire with maintaining the silencing effect within the range specified in a safety standard.

The muffler comprises an exhaust pipe 34 connected to a combustion chamber 36 of an internal combustion engine, a silencer 28 connected to an end part of the pipe 34, a punching pipe 40 arranged coaxially inside the silencer 28, and a diffuser disk 12 coaxially laminated at an exhaust port of the pipe 40. The disk 12 has its periphery forming a ring so as not to communicate with the outside in the predetermined range when laminated. Combustion gas coming from the combustion chamber 36 via the exhaust pipe 34 into the silencer 28 is made to pass into an adiabatic ventilation matter 42 via a vent 40a hole of the punching pipe 40, and exhaust from the range communicating with the outside toward the outside of the disk 12 after passing through an opening part 14 of each disk 12.