A light diffusive protective film for a surface light source device for protecting other base material and improving the luminance of information display is disclosed which comprises a transparent plastic film and a concave/convex layer stacked on the surface of the transparent plastic film and satisfies requirements that: (1) the ten-point mean roughness of the uneven surface in the concave/convex layer is 0.5 μm to 2.0 μm; and (2) the count number of profile peaks is 16 to 60 as determined by measuring a roughness curve for the uneven surface of the concave/convex layer and determining the count number of profile peaks by a peak count method.