This invention provides a methyl methacrylate resin light guide for use in a surface light source device. The methyl methacrylate resin light guide can reduce the occurrence of dark lines and can improve the screen image quality of a surface light source device. The light guide characterized by including a methyl methacrylate resin and fine particles. Herein, not less than 0.01 parts by mass and not more than 0.5 parts by mass of the fine particles are dispersed in 100 parts by mass of the methyl methacrylate resin. In addition, the absolute value of a difference in refractive index between the fine resin particles and the methyl methacrylate resin is not less than 0.001 and not more than 0.02, the fine resin particles have an average particle size of not less than 1 .mu.m and not more than 10 .mu.m.