The present invention discloses a controller for suppressing the temperature of a screen in order to maintain the ambient temperature of the screen to the level of a predetermined standard temperature as to avoid the screen from being operated at abnormal temperature and lowering its service life. The present invention utilizes a temperature detector unit connected to a control unit for detecting the ambient temperature and outputting a temperature signal to the control unit. The temperature signal is compared with the predetermined standard temperature to determine the magnitude of a cold cathode fluorescent lamp for suppressing the operation of the screen to the best ambient temperature and maintaining the normal service temperature.