To provide an internal combustion engine provided with a silencing exhaust device to improve scavenging efficiency by accelerating a velocity of flow of a flow of exhaust gas, discharged from a combustion chamber, to a high velocity of flow and provide a silencing effect.

This internal combustion engine comprises a branch chamber 2 having a front end part connected to the rear end of an exhaust pipe 1 and a flow cross section enlarged to a value higher than the of the exhaust pipe, acceleration parts 4a and 4b each having a front end part communicating with the rear end of the branch chamber and having a rear part the flow cross section of which is reduced at least by one stage, a negative pressure chamber part 5 having a front end part communicating with the rear end of the accelerating part and having a flow cross section increased to a value higher than that of the acceleration part, a bypass passage 9 to effect intercommunication between the branch chamber and the negative pressure chamber part, and silencing parts 19, 19a, and 19b situated in a flow passage in the rear of the branch chamber.