A navigation device includes an image sensor, a processing unit, a main clock circuit and an auxiliary clock circuit, wherein a clock frequency of the auxiliary clock circuit is much lower than that of the main clock circuit. The image sensor captures a predetermined number of image frames in a burst period. The processing unit is configured to calculate a displacement according to the image frames, to disable the main clock circuit after the predetermined number of image frames have been captured by the image sensor and to restart the main clock circuit with the auxiliary clock circuit before the end of the burst period.