3D television set or its external speaker box has container for a plurality of 3D spectacles. Container can locate individual 3D spectacles therein. Each of 3D spectacles has unique modulation reflector of infrared synchronizing signal. 3D television set displays 3D image on 3D program upon use of 3D spectacles detected directly by the modulation reflection or indirectly by 3D spectacles not remaining in container. 3D television set displays 2D image on 3D program if nonuse of 3D spectacles is detected directly by the no modulation reflection or indirectly by 3D spectacles remaining in container. Upon detection of nonuse, recommendation display is made to ware 3D spectacles. During 2D commercial message, synchronizing signal is halted. Recommendation to put unnecessary 3D spectacles in container is made upon end of every program, or end of 3D program followed by 2D program, or right before power off of 3D television set.