To propose a servo signal generating device, its method, and a disk device in which a servo characteristic having a sufficient phase margin can be obtained and a dynamic range can be expanded.

A servo signal generating device is provided with an A/D converter 2 for converting a servo signal to a digital signal with a sampling rate fs, a high band phase compensation circuit 21 for performing high band phase compensation with fs, a low band phase compensation circuit 23 for performing low band compensation with a sampling rate fs/N where N is an integer, an adder 26 for obtaining a servo signal by adding a high band signal and a low band signal, and a D/A converter 4 for converting a servo signal to an analog signal and outputting it. The high band phase compensation circuit 21, the low band compensation circuit 23, and the adder 26 are constituted with DSP 3, restore phase margin, and reduce operation errors in a low band.