1. A position and orientation measurement method comprising: an image input step of inputting an image from an image sensing device; an index detection step of detecting indices sensed in the image and acquiring information about image coordinates of the indices; a position and orientation calculation step of calculating a position and orientation of the image sensing device by using information about image coordinates of current indices detected from a current frame in the index detection step; a correction value calculation step of determining index appearance and/or disappearance between the current indices and past indices used to calculate the position and orientation of the image sensing device in a past frame and calculating position and orientation correction values to relax discontinuity in position and orientation estimated values between frames caused by the index appearance and/or disappearance; and a position and orientation correction step of correcting the position and orientation calculated in the position and orientation calculation step by using the correction values calculated in the correction value calculation step.