PURPOSE: To obtain an always uniform illuminating state without making an illumination spot appear on the design display part of a nameplate.

CONSTITUTION: As to this light guide plate for an instrument 1 guiding light L1 form a light source A to one direction; the light receiving surface 2a of the incident part 2 of the light guide plate 1 has such radius of curvature R1 and light receiving width T1 as the direct light L2 having light guiding width to cover all the area of the design display part D of the nameplate B, at least, is guided to the design illumination part 3 of the light guide plate, and is formed to be projected to the light source A. Then, the incident part 2 and the design illumination part 3 are formed to have the width equal to or larger than the light guiding width of the direct light L2.