1. A position/orientation measurement method for measuring a position and an orientation of a measurement target object, characterized by comprising: a captured image acquisition step of acquiring a captured image; an index detection step of detecting indices included in the captured image; a distribution range calculation step of calculating an evaluation value associated with a distribution range of the indices detected in the index detection step; and a position/orientation calculation step of calculating the position and the orientation of the measurement target object using information associated with image coordinates of the detected indices, and the evaluation value associated with the distribution range.