Magnetic disk device and method for switching bias voltage and drive voltage of microactuator

According to one embodiment, a magnetic disk device including a disk, a head that writes data to the disk and reads data from the disk, an actuator that is rotationally driven and controls movement of the head mounted above the disk, a microactuator that is mounted on the actuator and finely swings the head in a radial direction of the disk by a piezoelectric element that extends and contracts when a drive voltage based on a bias voltage is applied to the piezoelectric element, and a controller that switches the bias voltage according to an operation state during an access process.