A drive signal generating unit generates a drive signal used to alternately deliver a positive current and a negative current to a coil. A retractable bridge extension system is mechanically coupled to the bridgehead. In addition, a linear dielectric medium is located between individual nanopillars. The mark period constituted by the top pulse period and the intermediate bias period does not have a continuous part of a plurality of pulses having a small pulse width unlike a pulse train, so that the correct recording mark can be stably formed on the recording medium without an inadequate deformation of a recording pulse shape, even in the case of a high speed recording. The second composition is different from the first composition. To replace the switch, the switch’s housing is uncoupled from the controller’s housing to remove the switch unit and a new switch unit is coupled to the controller’s housing.