Magnetic disk device with recording head including spin torque oscillator

A magnetic disk device comprising:

• a disk-shaped recording medium including a magnetic recording layer;
• a recording head comprising a main magnetic pole generating a recording magnetic field to the magnetic recording layer, a write shield magnetic pole opposed to the main magnetic pole with a write gap to configure a magnetic core together with the main magnetic pole, a coil exciting a magnetic flux at the magnetic core, and a spin torque oscillator provided between the main magnetic pole and the write shield magnetic pole inside the write gap;
• and
• a controller comprising a record current supply circuit applying a record current to the coil and a drive current supply circuit supplying a drive current to the spin torque oscillator, the controller being configured to execute a process of monitoring variation of a resistance value of the spin torque oscillator while increasing the record current in a state in which the spin torque oscillator is energized, and executing and detecting a record current value when the resistance value is increased most largely so that an oscillation of the spin torque oscillator has occurred, and a process of setting the detected record current value to act as a lower limit of the record current supplied to the coil.