According to an embodiment of the disclosure, a lens assembly may include an image sensor, a first lens group disposed closest to an object side, the first lens group including multiple lenses and having negative power, a second lens group disposed to be moveable forward/backward along an optical axis direction, the second lens group having positive power, and a third lens group disposed to be moveable forward/backward along the optical axis direction, the third lens group including multiple lenses and having negative power, where the second or third lens group may move toward the object side so as to increase the focal length of the lens assembly, and the second lens group includes a lens having negative power and a lens having positive power and is disposed adjacent to the lens having negative power on the object side. In addition, various other embodiments may be possible.