A stereoscopic image display device including: a main display panel operable to alternately display a left image and a right image; an auxiliary display panel including first and second substrates having a pixel part corresponding to that of the main display panel and a sub-liquid crystal layer formed between the first and second substrates, and positioned in front of the main display panel to change polarization information of an incident left or right image; a plurality of first electrodes patterned on the first substrate along the rows of pixels formed on the main display panel; a second electrode formed on a front surface of the pixel part of the second substrate; and a light source to supply light to the rear side of the main display panel. Both a 3D vertical viewing angle and 2D luminance in a glass-type 2D display can be improved.