The present invention provides an air intake noise reducing device, an internal combustion engine fitted with the air intake noise reducing device and a structure for fitting the air intake noise reducing device to the internal combustion engine. The air intake noise reducing device comprises a gasket (2) comprising a ring member (2a) held by connecting surfaces of an air intake passage (100) and protrusion holding portions (2b) extending from the ring member (2a) toward a center of the air intake passage (100); and a net member (3) comprising a net (3a) for rectifying intake air and connecting protrusions (3b) extending outward from the net (3). The connecting protrusions (3b) are held in the protruding holding portions (2b) such that the ring member (3) is firmly secured to the gasket (3). The air intake noise reducing device constituted by in the above-mentioned manner can reduce assembly man-hours without deteriorating a sealing property of the air passage.