those when the constant a of the quadratic function is changed to 0 9 1 0 1 1 1 2 and 1 3 in the case of the parabola shape symbol c note that the horizontal axis of fig8 shows types 1 to 6 of illumination devices having light guide plates which are respectively formed by changing these numeric values as obvious from the experimental results of the anisotropy evaluation values of the luminance distribution of fig8 in the light guide plate configuration having the dot like reflective areas on the bottom surface of the symbol d the anisotropy evaluation value of the luminance distribution is about 0 98 which shows that there is more emission in the direction of u03c6 90 u00b0 than in the direction of u03c6 0 u00b0 in other words it shows that there is more emitted light in a direction parallel to a light propagation direction in the light guide plate and less emitted light in a direction orthogonal to the light propagation direction in contrast to this if the convex streak 8 of the emission surface 2 d is shaped like the lenticular lens symbol a the trapezoid symbol b and the parabola symbol c like the light guide plate 2 of the present invention and if the v shaped concave streaks 7 are formed on the bottom surface 2 c the anisotropy evaluation value of the luminance distribution is about 1 2 to 1 9 any of which is 1 or higher specifically it is indicated that if the light guide plate of the present invention is used there is more emission in the direction of u03c6 0 u00b0 than in the direction of u03c6 90 u00b0 in other words it is indicated that.