A lens assembly includes a lens having an optical portion and a flange portion at a periphery of the optical portion, a spacer having an incident hole through which light passes, and a lens barrel accommodating the lens and the spacer. The lens includes a first D-cut portion and a second D-cut portion formed on a side surface and another side surface of the flange portion in a state of non-contact with the lens barrel, and circular arc portions connecting the first and second D-cut portions to each other. The spacer includes blocking portions having a shape corresponding to a shape of the first and second D-cut portions, and first curved portions having a shape corresponding to a shape of the circular arc portions on an inner side surface, and transmission portions formed in locations in which the blocking portions and the first curved portions are connected to each other.