1. A method of generating a depth image, the method comprising: irradiating an object with light generated from a light source; acquiring a plurality of phase difference signals which have different phase differences from one another, by sensing a reflection light reflected from the object; generating a first depth image based on the plurality of phase difference signals; generating a second depth image based on phase difference signals in which a motion artifact has not occurred, among the plurality of phase difference signals; and generating a third depth image by combining the first depth image and the second depth image.