A method of preparing composite materials by (a) containing particulates to which an adhering material is to be made to adhere, in a rotary body having a bottom surface and a side wall; (b) rotating the rotary body so as to apply centrifugal forces to the particulates in the rotary body; and (c) varying the inclination of the rotary body to an arbitrary inclination angle in the range from an angle at which the bottom surface of the rotary body forms a horizontal surface perpendicular to the direction of gravity to an angle at which the bottom surface forms a vertical surface parallel to the direction of gravity, and supporting the rotary body at the arbitrary inclination angle