To improve silencing function, facilitate mounting operation, and prevent a muffler from falling off in absorbing exhaust noise of an air cylinder for buffering using a noise absorbing material.

A female screw 15 is formed in an exhaust hole 12 of a main cylinder 2. A noise absorbing material 16 is made of hard material such as urethane foam and a male screw 16a formed in the noise absorbing material 16 is screwed into the female screw 15 of the exhaust hole 12. Because volume of the noise absorbing material 16 can be increased independent of a size of the exhaust hole 12, silencing effect can be improved. Further, the noise absorbing material 16 itself is screwed, installation or removal can be facilitated, and the constitution of the muffler can be considerably simplified.