The invention has an object of providing a display device which can make a full use of a mirror functionality even in a dark environment. A display device comprising: image forming means (50, 60, 70, 71) for displaying information to be displayed during one state external light during the other state; input means (30) for inputting a mirror function executing instruction; and control means (82) for causing the image forming means to be switched to the other state in response to the mirror-function executing instruction. The display device further comprises an illumination unit (91) for irradiating an object to be reflected in the mirror (60) with light during the other state.