Between the bottom end of the front glass window and the top end of the dash panel constituting the front wall of the vehicle chamber is formed the cowl frame member extending in a transverse direction of the vehicle body. An air passage consists a first air passage section and a second air passage section and communicates the first air opening for introducing the open air with the second air opening for introducing the open air introduced from the first air opening into the vehicle chamber. The first air passage section is formed in a space within the cowl frame member while the second air passage section is formed outside the cowl frame member. Either one of the first and second air openings is formed in the cowl frame member in such a manner as being communicated with the first air passage section. The one of the first and second air openings and the first air passage section are positioned at an end portion of the cowl frame member in a transverse direction of the vehicle body.