A light control member formed by a prism sheet 5 is arranged along an emitting surface 12 of a light guide plate of a side light type surface light source device for liquid-crystal display backlighting arrangement and the like. The prism sheet 5 is provided with numerous projections formed with a height H1 at a pitch D1. Roughness is imparted to the emitting surface 12 by matt-processing or adhesion of fine particles. The roughness is preferably within the arithmetic average roughness Ra range 0.02-0.25 &mgr;m. Non-uniformity may be applied to height H1 of the prism sheet 5. The tendency of the prism sheet to adhere to the emitting surface is reduced and degradation of light quality prevented by the roughness of the emitting surface and/or non-uniform height of projections on the prism sheet.