perceptional characteristic fig5 is a schematic of an fed according to a second embodiment of the present invention hereinafter a second embodiment of the present invention will be described in detail with reference to fig5 for simplicity of description the same parts as in the first embodiment will be omitted fed 300 includes summator 310 for summating input video signals in line units divider 320 for calculating an average brightness level in line units lut 340 for storing a reference brightness level indicating the brightness of an image to be displayed and signals of the pwm clock signal condition according to each brightness level comparator 330 for comparing the average brightness level calculated by divider 320 with the reference brightness level of lut 340 to generate signals of the pwm clock signal condition line memory 350 for storing the input video signals in line units pwm clock signal generator 360 for generating pwm clock signals according to the result of the comparison driver 370 for driving a display panel and display panel 380 summator 310 receives video signals and horizontal synchronous signal hs to calculate the data capacity of the video signals in line units summator 310 summates one line i e 8 bit rgb data in the active interval of one horizontal synchronous signal hs the resultant value of the summation is sent to divider 320 that calculates the average in units of one frame divider 320 calculates the average of the 8 bit rgb data the average indicates the brightness of the video signals to be displayed namely.