To form a state where only a part of an emission surface appears to be emitting light.

An LED surface light-emitting device 10 is constructed in such a way that an incident surface 3a1 is configured with an end face of a substantially rectangular shaped light guide plate 3a; an emission surface 3a2a is configured with a top-side surface 3a2 of the light guide plate 3a; and a prism cut 3a3a1 is formed in a part 3a3a opposite to the emission surface 3a2a on a reverse-side surface 3a3 of the light guide plate 3a, the prism cut 3a3a1 being subjected to surface roughening process so that light emitted from an LED light source 1a, passed through the incident surface 3a1 and reflected by the prism cut 3a3a1 can reach the whole of the emission surface 3a2a. In this device, when the electricity conduction amount of the LED light source 1a changes from a low speed non-conducting state to a conducting state, states change from one where a root-side part 3a2a1 of the emission surface 3a2a appears to be emitting light to one where the emission surface 3a2a appears to be emitting light, and states change from one where a tip-side part 3a2a2 of the emission surface 3a2a appears to be not emitting light to one where the emission surface 3a2a appears to be emitting light.