PROBLEM TO BE SOLVED: To linearly vary colors of the entire image displayed in accordance with the amount of operation.SOLUTION: An endoscope processor 20 includes a memory 23 and a color space transform circuit 27. Original image signals of RGB received from an electronic endoscope 30 are housed in the memory 23. The original image signals housed in the memory 23 are transmitted to the circuit 27 in executing a color adjustment treatment. The circuit 27 transforms the original image signals to transformed image signals represented in a CIELAB uniform color space. The accumulated amount of change which linearly corresponds to the amount of operation to an input part 26 is added to signal components of the transformed image signals. The transformed image signals to which the accumulated amount of change is added are transformed to output image signals represented by RGB.
