PURPOSE: To reduce exhaust noise extending over a wide frequency region effectively by making an opening rate of influence bypass holes opened in the pipe of a silencer for an internal combustion engine larger toward downstream side so as to allow uniform interfering action.

CONSTITUTION: An inlet pipe 6, inner pipes 7, 8, and an outlet pipe 9 are provided in a resonance chamber 10 and enlarging chambers 11, 12, and exhaust gas is discharged through arrows B, C, the enlarging chamber 12, and the outlet pipe 9 in order. Bypass holes 14 in the inlet pipe 6 are provided at equal spaces in a range A, and in this case, the holes 14 having a diameter becoming larger toward a downstream side is formed. The amount of exhaust gas discharged from the bypass holes 14 becomes uniform extending over a wide distribution range and interference action is carried out in main gas flow uniformly extending over a wide frequency range. Thus, the exhaust noise is reduced extending over a wide frequency region.