The present invention provides an optical switch for making part of incident light, which has been made incident on an optical waveguide, selectively emergent to a light emergence portion provided outside the optical waveguide. The optical switch includes a liquid crystal device for selective emergence of the incident light. An arbitrary layer of the liquid crystal device is set such that letting .DELTA.n be a difference between a refractive index n.sub.o of the optical waveguide and a refractive index n.sub.1 of the arbitrary layer of the liquid crystal device, "d" be a thickness of the arbitrary layer, and .lamda. be a wavelength of the incident light, the values of .DELTA.n, "d", and .lamda. satisfy a condition of 2.20.times.10.sup.-3.ltoreq.|.DELTA.nd.lamda..sup.-1|.ltoreq.3.03.times.1- 0.sup.-3. With this optical switch, the uniformity of a light emergence efficiency can be easily realized by making use of a small change region in which the light emergence efficiency is not largely varied. The present invention also provides a display unit using the optical switches.