PROBLEM TO BE SOLVED: To reliably pick up a suspected lesion which has the possibility of lesion in screening.SOLUTION: A first special light image 100 obtained by combining an overall bright normal light image with a first blue-enhanced image in which blood vessels of an observation target and their structures are enhanced is obtained, and displayed on a display device 14. A suspected lesion such as a spot of the subject is detected from the first special light image 100 which is obtained. When the suspected lesion is found, an oxygen saturation level of the suspected lesion is obtained. When the oxygen saturation level of the suspected lesion is in a hypoxic condition within a predetermined range, an oxygen saturation level image 101 representing the oxygen saturation level by imaging is displayed instead of the first special light image 100 on the display device 14.【課題】病変である可能性が高い病変可能性部位をスクリーニング時に確実に拾い上げる。【解決手段】全体的に明るい通常光画像上に、観察対象の血管及び構造を明瞭化した第１青色強調画像を合成した第１特殊光画像１００を取得し、表示装置１４に表示する。取得した第１特殊光画像１００から、スポットなどの被検体上の病変可能性部位を検出する。病変可能性部位が検出されたら、その病変可能性部位の酸素飽和度を求める。求めた酸素飽和度が所定範囲の低酸素状態であれば、第１特殊光画像１００に代えて、酸素飽和度を画像化した酸素飽和度画像１０１を表示装置１４に表示する。【選択図】図２０
