PURPOSE: To prolong the life of a CRT display and to save electric power by automatically stopping the supply of a power source to the CRT display by a power source control means when an illuminance value measured by an illuminance measurement means is equal to or under a prescribed value.

CONSTITUTION: When a power source switch 5 is turned on, the power source for input 21 is supplied to a power source part 4 and the power source for a control part 22 is supplied to an illiminance sensor 2 and the power source control part 3 of the CRT display. Then, when the illuminance value of light irradiating a CRT screen is measured by the sensor 2, the illuminance value is inputted to the power source control part 3 of the CRT display. When it is judged by the power source control part 3 of the CRT display that a threshold value is equal to or under the prescribed value, the power source turning-off designation of the CRT display 1 is outputted to the power source part 4. Based on the designation, the power source part 4 automatically stops the supply of the power source 23 of the CRT display.