An air diffusion device inside a room of a building, in particular an animal breeding room, comprising: - a cylindrical body whose upper part constitutes an air intake and whose lower part comprises at least one air diffusion window which extends on its periphery, this window being provided with fins (229a, 229b, 229c), the device being characterized in that the window is provided with fins on at least two rows in height, the successive rows of fins from bottom to top being more and more inclined relative to the vertical, in that the device further comprises a closure member mounted to slide vertically inside the lower part of said body, this closure member comprising a vertical or substantially vertical cylindrical peripheral wall and a central closure disk closing off the space formed inside said cylindrical wall, the outside diameter of said cylindrical wall corresponding to the inside diameter of the lower part of said body within the nearest sliding clearance, in that said closure member is movable between a position called "rest" position, in which its peripheral wall is located opposite the diffusion window(s) of the body, so as to prevent the circulation of air from the upper part of the body through said diffusion window(s), and a position called "diffusion" position, in which its peripheral wall is no longer located opposite at least part of the surface of said diffusion window(s) of the body, so as to allow the circulation of air from the upper part of the body through said diffusion window(s), and in that the switching from the rest position to the diffusion position takes place against the gravitational force of a counterweight, when the pressure prevailing at the lower face of the closure disk is lower than the one prevailing at the upper face of said disk. - a cylindrical body whose upper part constitutes an air intake and whose lower part comprises at least one air diffusion window which extends on its periphery, this window being provided with fins (229a, 229b, 229c), the device being characterized in that the window is provided with fins on at least two rows in height, the successive rows of fins from bottom to top being more and more inclined relative to the vertical, in that the device further comprises a closure member mounted to slide vertically inside the lower part of said body, this closure member comprising a vertical or substantially vertical cylindrical peripheral wall and a central closure disk closing off the space formed inside said cylindrical wall, the outside diameter of said cylindrical wall corresponding to the inside diameter of the lower part of said body within the nearest sliding clearance, in that said closure member is movable between a position called "rest" position, in which its peripheral wall is located opposite the diffusion window(s) of the body, so as to prevent the circulation of air from the upper part of the body through said diffusion window(s), and a position called "diffusion" position, in which its peripheral wall is no longer located opposite at least part of the surface of said diffusion window(s) of the body, so as to allow the circulation of air from the upper part of the body through said diffusion window(s), and in that the switching from the rest position to the diffusion position takes place against the gravitational force of a counterweight, when the pressure prevailing at the lower face of the closure disk is lower than the one prevailing at the upper face of said disk.