Provided is a display device having a viewing angle changing function, which is capable of preventing leakage of information displayed on a display screen even when there is a fault generated in changing the viewing angle. The image display device including a viewing angle changing element capable of changing a wide vision display and a narrow vision display and including a display element is provided with a detection element which detects a fault generated in the viewing angle changing element and a module for changing to a narrow vision display when there is a fault based on a detection value of the detection element. For example, when there is a fault, a transparent heater is operated to heat a liquid crystal layer to set a transparent-scattering changing element to a transparent state and forcibly set the display device to a narrow vision display.