A magnetic disk unit comprises a record/reproduce head (2) that moves relative to a magnetic disk (26) rotating at a predetermined speed; an actuator (3) for positioning the magnetic disk (26) with respect to the head (2); and a controller (4) for detecting the head position using servo sectors storing position information recorded magnetically on a magnetic disk (1), thus controlling to position the actuator (3) according to the detected signal. The magnetic disk (1) comprises at least part where the track including servo sectors and data sectors is spiral.
