A surgery-assisting device comprising: a plurality of movable bodies operably connected to one another in order; and at least one actuator configured to generate a driving force that operates at least one of the movable bodies , wherein one of the plurality of movable bodies that is positioned at one end in a connecting direction includes a holding portion configured to hold a surgical instrument , at least one of the movable bodies that is positioned on a side of the surgical instrument in the connecting direction and that includes the movable body having the holding portion is provided as a distal-side movable body , at least one of the movable bodies that includes the movable body positioned farthest from the surgical instrument in the connecting direction and that is other than the distal-side movable body is provided as a proximal-side movable body , and supposing that a degree of tolerance for operation of the movable body when an external force other than the driving force of the actuator is applied to the movable body is operation tolerance which includes rotational operation tolerance and / or rectilinear operation tolerance, wherein the external force is an unexpected force of contact to the movable bodies to change the position and pose of the movable bodies , the operation tolerance of the distal-side movable body is set higher than the operation tolerance of the proximal-side movable body , characterized by comprising a connecting part in the distal-side movable body having a lower stiffness than a connecting part (30A, 30B, 30C1, 30C2) in the proximal-side movable body , wherein at least one pneumatic actuator configured to generate a driving force by a change in pressure of a gas and at least one electric actuator configured to generate a driving force by a motor are provided as the actuators, the proximal-side movable body is operated by the electric actuator , and the distal-side movable body is operated by the pneumatic actuator . a plurality of movable bodies operably connected to one another in order; and at least one actuator configured to generate a driving force that operates at least one of the movable bodies , wherein one of the plurality of movable bodies that is positioned at one end in a connecting direction includes a holding portion configured to hold a surgical instrument , at least one of the movable bodies that is positioned on a side of the surgical instrument in the connecting direction and that includes the movable body having the holding portion is provided as a distal-side movable body , at least one of the movable bodies that includes the movable body positioned farthest from the surgical instrument in the connecting direction and that is other than the distal-side movable body is provided as a proximal-side movable body , and supposing that a degree of tolerance for operation of the movable body when an external force other than the driving force of the actuator is applied to the movable body is operation tolerance which includes rotational operation tolerance and / or rectilinear operation tolerance, wherein the external force is an unexpected force of contact to the movable bodies to change the position and pose of the movable bodies , the operation tolerance of the distal-side movable body is set higher than the operation tolerance of the proximal-side movable body , characterized by comprising a connecting part in the distal-side movable body having a lower stiffness than a connecting part (30A, 30B, 30C1, 30C2) in the proximal-side movable body , wherein at least one pneumatic actuator configured to generate a driving force by a change in pressure of a gas and at least one electric actuator configured to generate a driving force by a motor are provided as the actuators, the proximal-side movable body is operated by the electric actuator , and the distal-side movable body is operated by the pneumatic actuator . <EOS>