Video signals are subjected to necessary signal processing by a video signal processing unit 1, subjected to conversion by an LUT unit 2 achieving a DICOM gamma characteristic, and output to a display unit 6. At this time, a CPU 3 refers to a memory 4 so as to read a decrement of luminance of a backlight 7 commensurate with an increment of screen luminance based on the output or an illumination sensor 5, thus instructing a backlight drive unit 8 to decrease the luminance of the backlight 7. This makes it possible to decrease the luminance of the backlight 7 by an increment of screen luminance owing to the brightness of the surrounding light. The CPU 3 corrects the black luminance reflecting a decrement of luminance of the backlight 7, thus updating the content of the LUT unit 2 achieving the DICOM gamma characteristic. Thus, it is possible to achieve good gray scale reproducibility irrespective of the influence of the surrounding light.
