A liquid crystal display includes a surface light source device of a side light type for lighting. On lighting a fluorescent lamp, primary light is introduced into a guide plate and propagates within the guide plate. Much of the illumination light enters into any one of a number of ridges on an emission-function face, being followed by inner impingement upon a flank face, which is more remote from an incidence end face, at an entry angle greater than a critical angle theta 1. Much of the light which has undergone such inner impingement is supplied to a liquid crystal display panel almost frontward via a top face. The ridges are inclined at a predetermined inclination angle alpha with respect to the incidence end face of the guide plate. Inclination angle alpha preferably falls within a range from 5 degrees to 45 degrees, in particular, from 15 degrees to 30 degrees. Employment of size-reduced ridges is realizable, leading to less conspicuous ridges without reducing emission function. Moire fringes are preventable, too. Each ridge may be provided with all or some of a tapered shape, an inclined flank face and foot portions with a stepwise difference.