To provide a surface light source uniformizing device allowing an illumination signboard or the like to uniformly shine in a panel and to have fine appearance while making a display screen very bright.

This surface light source uniformizing device comprises a transmitted light adjusting sheet 1 of rectangular shape provided with a light reflecting film 12 so as to have a large number of light transmission regions 11, and a light reflecting sheet 2 jointed to two opposed sides of the transmitted light adjusting sheet 1. The light transmission regions 11 of the transmitted light adjusting sheet 1 are so formed that the areas of the light transmission regions 11 are enlarged as they go away from the centerline, with respect to the areas of the light transmission regions 11 almost at the centerline parallel with two sides to which the light reflecting sheet 2 is jointed and that the areas of the light transmission regions 11 in the direction of the centerline are almost of the same degree.