Embodiments of the present invention effectively control utilizing a spoiler, the windage vibration of a magnetic head caused by the airflow generated in accordance with rotation of a magnetic disk, while reducing the dust flowing in on the downstream side of the spoiler. According to one embodiment, a spoiler is provided with wings facing a plurality of magnetic disks and a supporting section for the wings is disposed on the upstream side of a head stack assembly in the airflow direction in accordance with the rotation of the magnetic disks. Further, the wings each extend in a direction from the outer circumferences of the magnetic disks towards the spindle shaft while reducing the width of the wing, and is formed to have the width of the wing in a range of 2.7% through 2.9% of the circumferential length of the magnetic disks in a range of two thirds of the length of the wing in a direction towards the spindle shaft from a region located at the outer circumferences of the magnetic disks.