A ventilating system is proposed which comprises an air passage communicating between an outdoor side and an indoor side. In order to prevent noise entering from the outdoor side and sound escaping from the indoor side and to prevent outdoor air invading at wind speed over a specific value, a part of the air passage is defined by a hexagonal frame main body whose cross section is reduced gradually from outdoor side to indoor side. Further, it is provided a sound deadening member which is a hexagonal sound absorbing cone member comprising an outside sound deadening portion which is a first hexagonal cone whose apex is directed to the outdoor side and an inside sound deadening portion which is a second hexagonal cone whose apex is directed to the indoor side, so that the cross section of the air passage is reduced gradually from the apex of the first hexagonal cone to a bottom surface portion thereof and increased gradually from the bottom surface portion thereof to the apex of the second hexagonal cone. Furthermore, an opening and shutting mechanism is provided in the air passage to close the air passage when wind speed of the outdoor side exceeds a specific value.