An illuminator includes a strip-shaped light guide and a plurality of light sources. The light sources are disposed along one end surface in the width direction of the light guide to allow light to be incident on the one end surface. The light guide guides the light of the light sources from the one end surface to the other end surface in the width direction of the light guide. The one end surface and the other end surface of the light guide are light-diffusing surfaces. The width of the light guide is larger than the thickness of the light guide.