A navigation device including an image sensor, a processor and a memory is provided. The memory stores a lookup table of a plurality of frame rates each corresponding to one frame period extender. The image sensor captures a pair of image frames. The processor calculate a current displacement according to the pair of image frames, read a next frame period and a corresponding frame period extended value from the memory according to the calculated current displacement, and insert an inactive period after the pair of image frames when the frame period extended value is larger than 1 and the current displacement is larger than a displacement threshold.