A surgery assisting apparatus comprises: a distance measuring unit configured to measure a distance to an object in a body cavity； a hollow tube including a cylindrical portion to be partially inserted into the body cavity and a portion that performs distance measurement by the distance measuring unit, the hollow tube enabling distance measurement in a given position on a circumference at a predetermined distance from a major axis of the cylindrical portion； and a controller configured to control the position on the circumference around the major axis where the distance measuring unit performs distance measurement, such that approach of a medical instrument inserted into the body cavity to the object is sensed, wherein the controller controls the position on the circumference around the major axis in accordance with an advancing direction of a distal end of the medical instrument.
