1. A position/orientation determination method for determining a position and an orientation of a target object, the position/orientation determination method comprising: an image input step of inputting a shot image obtained from an imaging device attached to the target object; an orientation input step of inputting a measured orientation obtained from an orientation sensor which acquires information regarding the orientation of the target object; an index detection step of obtaining image coordinates of indices arranged on a scene from the shot image as measured image coordinates; and a calculation step of calculating parameters including the position of the target object with regard to inclination angles of the measured orientation of the target object as being within an allowable range, the parameters being calculated such that errors between the measured image coordinates being obtained in the index detection step and their theoretical values being obtained on the basis of the measured orientation and estimated parameters are reduced, using image Jacobians of the theoretical image coordinates with respect to the parameters.