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 first phase difference images based on the plurality of phase difference signals; generating a first depth image based on the first phase difference images, wherein the first depth image comprises a motion artifact; generating second phase difference images based on phase difference signals, from among the plurality of phase difference signals, in which the motion artifact has not occurred; generating a second depth image based on the second phase difference images, wherein the second depth image comprises an offset effect; and generating a third depth image by combining the first depth image and the second depth image.