PURPOSE: To heighten the volumetric efficiency based on inertial supercharging, by providing a resonance pipe with a bell-mouthed part connected to a resonance vessel constituting an intake manifold.

CONSTITUTION: A resonance pipe 5 is provided with a bell-mouthed front-end part connected to a resonance vessel 4. The area A2 of the cross section of the bell-mouthed part on the vessel 4 and that A1 of the cross section of the bell- mouthed part on the pipe body 5 are related to each other as 1.9≤A2/A1≤4.0. The sum V of the volumes of the resonance vessel 4, an intake pipe and a cylinder, the synchronous revolution speed Nt and the sum VH of stroke volumes of cylinders connected to one vessel are related to each other as 0.5≤V/VH≤2 and 0.24≤A1/VH.Nt≤0.7. As a result, the resistance to the inflow or outflow to or from the resonance pipe 5 is reduced to heighten the volumetric efficiency based on inertial supercharging.