Embodiments of the invention prevent a magnetic head from coming into contact with a protrusion on a magnetic disk. In one embodiment, a head gimbal assembly includes a piezoelectric actuator for changing the flying height of a head/slider assembly. The address of a protrusion on a magnetic disk is preregistered in a nonvolatile memory. When a seek operation or following operation is to be performed, the head/slider assembly flies at a reference flying height. Before the protrusion passes below the head/slider assembly, an operating voltage is applied to the piezoelectric actuator to increase the flying height. After the protrusion passes below the head/slider assembly, the head/slider assembly flies at the reference flying height with operating voltage application stopped.