Linear driving mechanism with self-weight compensation, operation input device, and surgery assistance system

A linear driving mechanism with self-weight compensation comprising:

• a holding member that holds
• a first moving body to which an object is attached,
• a second moving body provided with a weight, and
• a coupling portion that couples the first moving body to the second moving body so that the weight moves with a directional component in a direction opposite to a movement direction of the first moving body,
• wherein the holding member is capable of rotating around a rotation axis, and
• wherein when a mass of the first moving body in a state where the object is attached is defined as M1, a mass of the second moving body is defined as M2, a distance between a first intersection point of a perpendicular line from a rotation center of the rotation axis to the first moving body and a first gravity center of the first moving body when the distance between the first intersection point and the first gravity center in the first moving body is the shortest is defined as L1, and a distance between a second intersection point of a perpendicular line from the rotation center of the rotation axis to the second moving body and a second gravity center of the second moving body when the distance between the second intersection point and the second gravity center in the second moving body is the shortest is defined as L2, M2=(L1/L2)×M1 is satisfied.