Image signals outputted from a CCD to an image signal processing circuit, which performs A/D conversion, YC signal processing to convert the image signals into video signals of NTSC or the like and outputs video signals after D/A conversion. A microcomputer receives the video signals from the image signal processing circuit and determines a brightness level of the video signals. An EEPROM stores a data table showing the relationship between a correction amount and the brightness level, and the microcomputer obtains the correction amount from the EEPROM. The microcomputer corrects the video signals according to the correction amount before the D/A conversion, and the image signal processing circuit outputs the corrected video signals to a displaying device controlling circuit, and a displaying device displays an image.