PROBLEM TO BE SOLVED: To provide a magnetic disk device suitably used for high-speed accessing by reducing the size and the weight of a magnetic disk supporting mechanism. SOLUTION: One end of a supporting part 3 is held by a rotatable rigid arm part 4, and a pneumatic pressure adjusting means 7 formed by shaping the supporting part itself is provided in the opposing surface of a magnetic disk 1 near the free end of the supporting part. A magnetic head 2 is attached to a magnetic head attaching part 31 roughly perpendicular to the positive pressure generating part 71 of the pneumatic pressure adjusting means provided in the free end of the supporting part. The positive pressure generating part 71 is composed of a tapered part 711 and a flat part 712, an air spring is formed by its relative motion with a magnetic disk, and the magnetic head is caused to float by a floating amount matching ahead pressing load generated based on the rotational angle θ of the supporting part. By changing the rotational angle θ, an optional floating amount, or a contact surface pressure with the magnetic disk, is obtained.