According to one embodiment, an optical device includes a first light-modulating element transmitting or scattering light, and a second light-modulating element transmitting or scattering the light passing through the first light-modulating element, a driving module alternately performing a first mode of making the first light-modulating element scatter the light and making the second light-modulating element transmit the light, and a second mode of making the first light-modulating element transmit the light and making the second light-modulating element scatter the light.