PROBLEM TO BE SOLVED: To surely correct differences among light distributions, which are caused in application of a plurality of kinds of irradiation light beams different in wavelength, even when observation conditions such as a subject distance are changed during endoscopic diagnosis.SOLUTION: A wavelength-variable element makes reflected light and the like from a subject separated into narrowband light beams with a wavelength making an extinction coefficient of oxygenated hemoglobin (HbO2) and that of reduced hemoglobin (Hb) different from each other, and makes the reflected light and the like from the subject separated into narrowband light beams with a wavelength making the extinction coefficient of oxygenated hemoglobin (HbO2) and that of reduced hemoglobin (Hb) equal to each other. Three or more image signals are obtained by taking an image of each separated light beam by an image sensor. The image signal, which is used for generation of an oxygen saturation image, among the image signals is corrected to eliminate differences among signal distributions, which are caused by the differences among the light distributions of the narrowband light beams. Since correction is performed by using correction data obtained from the image signal with the wavelength making the extinction coefficient of oxygenated hemoglobin and that of reduced hemoglobin equal to each other, oxygen saturation information borne by the image signal is not erased.【課題】被写体距離などの観察条件が内視鏡診断中に変化したとしても、波長が異なる複数種類の照明光を照射したときに生ずる配光分布の違いを確実に補正する。【解決手段】被検体からの反射光等は、波長可変素子によって、酸化ヘモグロビン（ＨｂＯ２）と還元ヘモグロビン（Ｈｂ）の吸光係数に違いがある波長を有する狭帯域光に分光されるとともに、酸化ヘモグロビン（ＨｂＯ２）と還元ヘモグロビン（Ｈｂ）の吸光係数が等しい波長を有する狭帯域光に分光される。分光毎に撮像素子で撮像して３以上の画像信号を得る。これら画像信号のうち、酸素飽和度画像の生成に用いられる画像信号は、各狭帯域光間の配光分布の違いによる信号分布の違いが無くなるように補正される。補正は、酸化ヘモグロビンと還元ヘモグロビンの吸光係数が等しい波長の画像信号から得られる補正データを用いて行われるため、画像信号に乗っている酸素飽和度の情報を消すことが無い。【選択図】図６
