Provided is an endoscopic surgical apparatus which can easily obtain an image desired by an operator and has high operability. The endoscopic surgical apparatus includes an outer tube main body 302 that is inserted into a body cavity through a body wall, an endoscope insertion passage 304 provided in the outer tube main body 302, and an outer tube main body 302. A treatment instrument insertion passage 306 provided inside, a position sensor 310 that detects the amount of movement of the treatment instrument insertion section 202 relative to the outer tube main body 302 when the treatment instrument insertion section 202 moves forward and backward, and a treatment instrument by the position sensor 310 When the movement amount of the insertion unit 202 is detected, if the movement amount of the treatment instrument insertion unit 202 is within a predetermined range, a dead zone region that does not change the range of the observation image obtained by the endoscope 100, and the treatment tool insertion A control unit 314 that changes the range of the observation image in accordance with the amount of movement of the treatment instrument insertion unit 202 when the amount of movement of the unit 202 is not within the predetermined range.術者が望む画像を簡単に得られ、操作性の高い内視鏡下外科手術装置を提供する。内視鏡下外科手術装置は、体壁を貫通して体腔内に挿入される外套管本体302と、外套管本体302の内部に設けられた内視鏡挿通路304と、外套管本体302の内部に設けられた処置具挿通路306と、処置具挿入部202が進退移動したときにおける外套管本体302に対する処置具挿入部202の移動量を検出する位置センサ310と、位置センサ310によって処置具挿入部202の移動量が検出されたとき、処置具挿入部202の移動量が所定範囲内である場合には内視鏡100によって得られる観察画像の範囲を変化させない不感帯領域と、処置具挿入部202の移動量が所定範囲内でない場合には処置具挿入部202の移動量に応じて観察画像の範囲を変化させる制御部314と、を備える。
