A magnetic or optical disk apparatus having a flexible disk rotated at high speed and head sliders for reading and writing information on the disk, floating from both sides of the disk. The disk apparatus is also provided with straightening plates for keeping air flow in the radial direction of the disk as a laminar flow to surely prevent the disk from being vibrated at the time when the disk is rotated at high speed. As the result, positions of the head sliders relative to the disk can be surely and accurately maintained to provide heads with excellent recording and reproducing characteristics. Mass storage and high speed access can be thus achieved without damaging the flexible disk and the disk apparatus can be smaller-sized with lighter weight and lower cost.