A stereoscopic image display device includes a flat panel display unit, a lens array unit, and a light guide structure unit. The light guide structure unit includes a light guide microstructure. The light guide microstructure is disposed on a side of the lens array unit. A bottom angle of the light guide microstructure is defined as B, and a bottom length of the light guide microstructure is defined as P. The bottom angle B and the bottom length P of the light guide microstructure satisfies following conditions: (i) 15.5 degrees≤B≤83.5 degrees; and (ii) 10 micrometers≤P≤2,000 micrometers, such that an oblique viewing angle of the stereoscopic image display device falls within a range from 10 degrees to 60 degrees.