Abstract: A muffler includes a box-shaped member formed so as to define an inner space therein, and including at least two communication ports. An inner pipe is accommodated in the box shaped member, and includes a fluid passage formed therein. An end of the inner pipe is installed to one of the communication ports, and another end thereof is installed to another one of the communication ports. A separation is provided in the inner pipe which communicates the fluid passage with the inner space. The inner pipe can include a first tubular member, a part thereof formed integrally with the body by injection molding, and a second tubular member having an end. The end is disposed in the inner space so as to face an end of the first tubular member in spaced relation so as to form the separation. A guide and a fixing member can be formed on an inner wall surface of the body so as to connect the inner pipe with the communication port.