An endoscope apparatus (1, 1B, 1C) comprising: illumination means (13, 27) adapted to illuminate a body cavity interior; image pickup means adapted to pick up an image of the body cavity interior under illumination by the illumination means (13, 27); a mode changeover switch that is capable of switching between white light and illuminating light of narrow band wavelength illuminated from the illumination means (13, 27); first color separation means adapted to separate the image picked up by the image pickup means into a first luminance signal (Yh) and a first color difference signal (Cr, Cb); first color conversion means adapted to convert signals based on the first luminance signal (Yh) and the first color difference signal (Cr, Cb), respectively, to first three primary color signals; and second color conversion means adapted to convert three primary color signals based on an output signal from the first color conversion means to a second color difference signal (R-Y, B-Y); characterized in that the endoscope apparatus (1, 1B, 1C) further comprises: signal intensity ratio calculation means adapted to calculate an intensity ratio of the first three primary color signals outputted from the first color conversion means; a table adapted to be used for reference to set matrix coefficients to be used to perform a matrix calculation for color separation of a color difference signal based on the second color difference signal (R-Y, B-Y) converted by the second color conversion means; control means adapted to dynamically change the matrix coefficients, based on the intensity ratio calculated by the signal intensity ratio calculation means; and second color separation means adapted to convert a signal based on the first luminance signal (Yh) and signals based on an output signal (R-Y, B-Y) from the second color conversion means to second three primary color signals by performing the matrix calculation for the color separation to each of the signals based on the first luminance signal (Yh) and the output signal (R-Y, B-Y) from the second color conversion means, based on the matrix coefficients dynamically changed by the control means. illumination means (13, 27) adapted to illuminate a body cavity interior; image pickup means adapted to pick up an image of the body cavity interior under illumination by the illumination means (13, 27); a mode changeover switch that is capable of switching between white light and illuminating light of narrow band wavelength illuminated from the illumination means (13, 27); first color separation means adapted to separate the image picked up by the image pickup means into a first luminance signal (Yh) and a first color difference signal (Cr, Cb); first color conversion means adapted to convert signals based on the first luminance signal (Yh) and the first color difference signal (Cr, Cb), respectively, to first three primary color signals; and second color conversion means adapted to convert three primary color signals based on an output signal from the first color conversion means to a second color difference signal (R-Y, B-Y); characterized in that the endoscope apparatus (1, 1B, 1C) further comprises: signal intensity ratio calculation means adapted to calculate an intensity ratio of the first three primary color signals outputted from the first color conversion means; a table adapted to be used for reference to set matrix coefficients to be used to perform a matrix calculation for color separation of a color difference signal based on the second color difference signal (R-Y, B-Y) converted by the second color conversion means; control means adapted to dynamically change the matrix coefficients, based on the intensity ratio calculated by the signal intensity ratio calculation means; and second color separation means adapted to convert a signal based on the first luminance signal (Yh) and signals based on an output signal (R-Y, B-Y) from the second color conversion means to second three primary color signals by performing the matrix calculation for the color separation to each of the signals based on the first luminance signal (Yh) and the output signal (R-Y, B-Y) from the second color conversion means, based on the matrix coefficients dynamically changed by the control means. signal intensity ratio calculation means adapted to calculate an intensity ratio of the first three primary color signals outputted from the first color conversion means; a table adapted to be used for reference to set matrix coefficients to be used to perform a matrix calculation for color separation of a color difference signal based on the second color difference signal (R-Y, B-Y) converted by the second color conversion means; control means adapted to dynamically change the matrix coefficients, based on the intensity ratio calculated by the signal intensity ratio calculation means; and second color separation means adapted to convert a signal based on the first luminance signal (Yh) and signals based on an output signal (R-Y, B-Y) from the second color conversion means to second three primary color signals by performing the matrix calculation for the color separation to each of the signals based on the first luminance signal (Yh) and the output signal (R-Y, B-Y) from the second color conversion means, based on the matrix coefficients dynamically changed by the control means.