Magnetic disk device capable of correcting servo demodulation position

A method of correcting a servo demodulation position, which is applied to a magnetic disk device including a disk including two first servo sectors arranged side by side in a circumferential direction and at least a second servo sector located between the two first servo sectors, and a head that writes data to the disk and reads data from the disk, wherein the first servo sector includes burst data and a first data pattern written before the circumferential direction of the burst data, and the second servo sector includes the burst data, the first data pattern written before the circumferential direction of the burst data, and a second data pattern written after the circumferential direction of the burst data, the method comprising:

• demodulating the second data pattern to acquire a first phase of the second data pattern;
• calculating a difference value between the first phase and a reference phase;
• and
• correcting the servo demodulation position demodulated from the second servo sector when an absolute value of the difference value is equal to or larger than a threshold value.