This invention includes an arm main body (30) configured to move the distal end portion in a three-dimensional space with respect to the proximal end portion, a translation arm (35) including a proximal end side link (61) having a proximal end portion continuous with the distal end portion of the arm main body and configured to pivot about a first axis (L1) orthogonal to a predetermined reference direction (D) and pivot within an angular range including a retraction angular position (P1) and an advancement angular position (P2) at which the distal end portion is located on a side farther from the first axis than the retraction angular position in the reference direction, and a distal end side link (62) having a proximal end portion continuous with the distal end portion of the proximal end side link and configured to pivot about a second axis (L2) parallel to the first axis and pivot within an angular range including a closing angular position (P3) and an opening angular position (P4) forming a larger angle with the proximal end side link than an angle formed at the closing angular position, a translation arm drive unit (47) configured to cause the proximal end side link and the distal end side link to pivot with the driving force of the translation arm drive unit, and an instrument holder (36) configured to be continuous with the distal end portion of the translation arm and to hold a surgical instrument including a long-axis shaft (43) and a treatment tool (44) provided at the distal end portion of the shaft in a posture in which the shaft extends in the reference direction.本發明包括：臂本體(30)，使前端部相對於基端部於三維空間內移動；平移臂(35)，具有基端側連桿(61)及前端側連桿(62)，上述基端側連桿(61)構成為基端部與臂本體之前端部相連，繞與既定之基準方向(D)正交之第1軸線(L1)旋動，於包含退避角度位置(P1)、及前端部位於在基準方向上較退避角度位置更遠離第1軸線之側之進出角度位置(P2)的角度範圍內旋動，上述前端側連桿(62)構成為基端部與基端側連桿之前端部相連，繞與第1軸線平行之第2軸線(L2)旋動，且於包含縮閉角度位置(P3)、及與基端側連桿所成之角之角度較縮閉角度位置更大之擴開角度位置(P4)的角度範圍內旋動；平移臂驅動部(47)，藉由該驅動力使基端側連桿及前端側連桿旋動；以及器具保持部(36)，與平移臂之前端部相連，能夠將具有長軸狀之長柄(43)及設置於長柄之前端部之處理具(44)之外科用器具以長柄沿基準方向延伸之姿勢加以保
