An air intake includes a spike and a cylindrical cowl. The spike is composed of a plurality of plates which are arranged axial symmetrically around a central axis thereof, and the cowl includes an inner wall parallel to the central axis and is formed so as to enclose a rear portion of the spike via a given space. The adjacent ones of the plates form respective aerodynamic compressive surfaces in spaces formed by the adjacent ones. The distances between the adjacent ones of the plates are variable, and the distance between the forefront of the spike along the central axis and the cowl is variable.