A surgery assisting apparatus for controlling a posture of a first surgical tool to be inserted into a body cavity and mechanically driven, by using a second surgical tool to be inserted into the body cavity, comprises: a mode switch configured to switch a first mode and a second mode, the second surgical tool being used to control the first surgical tool in the second mode; one or more sensors configured to measure an angle and depth of insertion of a shaft of the second surgical tool into the body cavity; and at least one memory and at least one processor which function as a computing unit configured to determine a target position of a control point that is a point for specifying the posture of the first surgical tool in order to control the posture of the first surgical tool.