A display device comprising: a power supply unit configured to supply power to components of the display device; a communication unit configured to perform communication; a touch-screen unit configured to display an image and to receive a touch operation; and a control unit configured, upon detecting that a first condition is satisfied, to switch the display device to a first operation mode in which the power supply unit refrains from supplying power for enabling the touch-screen unit to receive a touch operation to the touch screen unit, while the touch-screen unit maintains a displayed image, and the power supply unit supplies power to the communication unit; wherein the touch-screen unit is configured to consume power to rewrite a displayed image and to consume no power to maintain a rewritten image, the display device further comprising a measuring unit configured to measure a position of the display device, a detecting unit configured to detect an event, characterised in that the event is the detection of measurement of a predetermined position of the display device, and wherein in the first operation mode, the control unit is configured, in response to detection of the event, to cause the power supply unit temporarily to supply power to the touch-screen unit to cause the touch-screen unit to rewrite the displayed image to another image according to the position measured by the measuring unit, and wherein the control unit is further configured, upon detecting that a second condition is satisfied, to switch the display device to a second operation mode in which the power supply unit supplies power to the touch-screen unit and the communication unit, wherein in the second operation mode, the power supply unit is configured to not supply power to the measuring unit, and the control unit is configured to perform an event update display, which causes the touch-screen unit to rewrite an image in response to detection of the event by the detecting unit, not an operation display, which causes the touch-screen unit to rewrite an image in accordance with a user's operation, and the control unit is configured to cause the touch-screen unit to display a current time image, and to rewrite the current time image in response to detection of a change in time by the detecting unit. a power supply unit configured to supply power to components of the display device; a communication unit configured to perform communication; a touch-screen unit configured to display an image and to receive a touch operation; and a control unit configured, upon detecting that a first condition is satisfied, to switch the display device to a first operation mode in which the power supply unit refrains from supplying power for enabling the touch-screen unit to receive a touch operation to the touch screen unit, while the touch-screen unit maintains a displayed image, and the power supply unit supplies power to the communication unit; wherein the touch-screen unit is configured to consume power to rewrite a displayed image and to consume no power to maintain a rewritten image, the display device further comprising a measuring unit configured to measure a position of the display device, a detecting unit configured to detect an event, characterised in that the event is the detection of measurement of a predetermined position of the display device, and wherein in the first operation mode, the control unit is configured, in response to detection of the event, to cause the power supply unit temporarily to supply power to the touch-screen unit to cause the touch-screen unit to rewrite the displayed image to another image according to the position measured by the measuring unit, and wherein the control unit is further configured, upon detecting that a second condition is satisfied, to switch the display device to a second operation mode in which the power supply unit supplies power to the touch-screen unit and the communication unit, wherein in the second operation mode, the power supply unit is configured to not supply power to the measuring unit, and the control unit is configured to perform an event update display, which causes the touch-screen unit to rewrite an image in response to detection of the event by the detecting unit, not an operation display, which causes the touch-screen unit to rewrite an image in accordance with a user's operation, and the control unit is configured to cause the touch-screen unit to display a current time image, and to rewrite the current time image in response to detection of a change in time by the detecting unit.