An internal combustion engine is disclosed which includes active cylinders which are always active and inactive cylinders which are inactive when the engine load is below a predetermined value. The engine has an intake passage divided into first and second branches connected to active and inactive cylinders, respectively. The second branch is provided near its inlet with a stop valve and is connected through an EGR passage to the engine exhaust passage. Means are provided to attenuate pressure waves resulting from exhaust pulsations and propagated through the EGR passage toward the second intake passage branch.