A head slider including a disk-facing surface having an inflow end and outflow end, inflow-end-side rail, negative pressure part, three extension rails, a pair of siderails, an inflow-end-side-positive-pressure part, and outflow-end-side-positive-pressure part, and an outflow end rail. The extension rails protrude towards the negative pressure part, and are formed lower than the inflow-end-side-positive-pressure part. As a result of air flowing in from the inflow end, a positive pressure (flotation force) is imparted to the inflow-end-side-positive-pressure part, and a negative pressure is imparted to the negative pressure part. The negative pressure which cancels the positive pressure acts to a suitable extent without being affected by atmospheric pressure variations, so the flotation amount is controlled to a fixed value regardless of variations of altitude (atmospheric pressure).