The invention discloses a 3D image display device and a dual-mode image display device. The 3D image display device comprise a polarized light source module, an image display unit, and a grating unit interposed therebetween comprising a dispersed liquid crystal unit, a micro-phase difference unit, and a polarizing film. The liquid crystal in the grating unit is controlled to switch between a dispersed state and a transparent state, so that images are switchably displayed in a flat image mode and a stereo image mode. Alternatively, the dispersed liquid crystal unit can be omitted, so that the display unit functions in a stereo image mode.