A magnetic disk device is provided with a magnetic head slider mounted with a magnetic head and a magnetic disk, and the magnetic head slider has the possibility of contacting the magnetic disk at the vicinity of the magnetic head during operation of the magnetic disk device. The magnetic head slider is 1.25 mm or less in length, 1 mm or less in width and 0.3 mm or less in thickness, and the friction force exerted between the magnetic head slider and the magnetic disk is 10 mN or less. The magnetic head comprises four substantially parallel surfaces, and the depth from a first surface, which is the most adjacent surface to the magnetic disk, to a second surface is 10 nm to 50 nm, the depth from the second surface to a third surface is 50 nm to 200 nm, and the depth from the third surface to a fourth surface is 400 nm to 1 &mgr;m.