An input coupler includes: a plurality of semi-reflectors located along an optical path along which a light incident from a light source travels, each of the plurality of semi-reflectors comprising a reflective surface that is inclined with respect to the optical path and configured to reflect a first portion of the light and transmit a second portion of the light; and a plurality of optical path changing members configured to change an optical path of the light transmitted through the plurality of semi-reflectors, wherein the plurality of semi-reflectors and the plurality of optical path changing members are arranged such that the light passing through at least one of the plurality of semi-reflectors and emitted in one direction has a linear beam distribution.