and it is amplified by the output amplifier 17 for display by the monitor 18 at the third time the third picked up still image data d3 is added to the first to second integrated still image data d1 d2 stored in the image memory 4 and the still image data d1 d2 d3 is stored into the image memory 4 it is also supplied to the pallet ram 14 since the pallet ram 14 is now set such that the output thereof is 1 3 of the input thereto the pallet ram 14 outputs the 8 bit still image data d1 d2 d3 3 to the d a converter 6 and it is amplified by the output amplifier 17 for display by the monitor 18 at the fourth or subsequent time the latest still image data is similarly added by the adder 3 to the still image data previously integrated and stored in the image memory 4 and the summed still image data is stored in the image memory 4 and also supplied to the pallet ram 14 in the pallet ram 14 the output is reduced for each integration in accordance with the number of times n of integration so that the 8 bit still image data is always supplied to the d a converter 6 the still image data is amplified by the output amplifier 17 and displayed on the monitor 18 since the integrated still image data is reduced for each integration in accordance with the current number.