Provided is an expansion-chamber muffler as a downsized sound muffler while keeping a function of noise reduction, comprising: a tube (A) which supplies and evacuates a gas having a noise, wherein the tube (A) in the midway has a cavity with a cross-sectional area larger than that of the tube (A)； and at least two or more ports for inflow or outflow of the gas on the lateral side of a tube (B) extending from the expansion-chamber muffler, on the opposite side of the noise source generating the noise.
