A control unit of a display device controls the display device in a normal mode of operation to operate in a normal state. The control unit controls the display device to enter into an anti-crime security mode of operation, when a state representing that the external information processing device may not be currently used is determined. The control unit cancels the anti-crime security mode of operation, when the information indicative of an authorized user for confirmation has been entered through the operation buttons by a user in the anti-crime security mode of operation. The control unit controls the display device to operate in an alarm mode of operation, when information indicative of the authorized user for confirmation has not been entered by a user in the anti-crime security mode of operation. The control unit performs an alarm operation in the alarm mode of operation.