PURPOSE: To prolong the life of a display device to a max. by judging the instruction generated by an external displaying setting means with a judging means, and turning on/off the switching means.

CONSTITUTION: When an external display setting means 11 issues the instruction of a display request, a judging means 9 judges it is the instruction of the display request, outputs the output signal of an ON-instruction to a switch driving control means 8, the switch driving control means 8 turns on a switching means 4, when the external display setting means 11 issues the instruction of undisplay request, the judging means 9 outputs the output signal of an OFF-instruction to the switch driving control means 8, and the switch driving control means 8 switches the switching means 4 from ON to OFF condition. Thus, by suitably setting the instruction of the external display setting means with a user, the user can put on a power source only at a necessary time for the user, can cut off it at the unnecessary time, and the life of the display device can be prolonged to the max.