PROBLEM TO BE SOLVED: To provide a mechanism for reducing a sense of visual field interference caused because a treatment instrument gets close to an imaging part, in a three-dimensional endoscope apparatus.SOLUTION: A three-dimensional endoscope apparatus includes an operable treatment instrument, at least two imaging means for photographing a target object, and watermark synthesis means for synthesizing images in such a manner that the image of a first area and the image of a second area, in which the treatment instrument within the second image taken by the other one of a plurality of imaging parts is not copied, are superimposed on each other at a predetermined synthesis ratio, in the first area in which the treatment instrument within the first image taken by one of the imaging means is copied.【課題】立体内視鏡装置において、処置器具が撮像部に近接することによる視野妨害感を軽減する仕組みを提供する。【解決手段】操作可能な処置器具と、対象物体を撮影する少なくとも２つの撮像手段と、撮像手段の一方で撮影された第１の画像内の処置器具が写っている第１の領域において、第１の領域の画像及び複数の撮像部の他方で撮影された第２の画像内の処置器具が写っていない第２の領域の画像を、所定の合成比率で重ね合せて画像合成する、透かし合成手段とを備える立体内視鏡装置。【選択図】図１
