According to one embodiment, a disk device rotates a disk information storage medium to record and reproduce information on the information storage medium by use of a head that slides in contact with a lubricant coated on the information storage medium, wherein a sliding speed U, area A and normal force N are set to cause U×A/N to fall within a monotonously increasing region in which a coefficient of friction associated with a frictional force occurring in a contact area of the head that faces the information storage medium monotonously increases as U×A/N increases, where the sliding speed U represents a sliding speed at a sliding time of the head, the area A represents the contact area of the head, and the normal force N represents a normal force applied to the contact area of the head.