According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head, an actuator, a controller, and a ramp. The magnetic head is configured to record data on and reproduce data from the magnetic disk. The actuator is configured to move the magnetic head relative to the magnetic disk. The controller is configured to control the actuator. The ramp is configured to hold the magnetic head. The controller is configured to, in a retract operation for causing the actuator to retract the magnetic head to the ramp, alternate detection of a back electromotive force of the actuator and application of a voltage corresponding to the back electromotive force to the actuator, and skip the detection of the back electromotive force a predetermined number of times in response to an event that the magnetic head moves at a speed outside a predetermined range.