1. A position detecting method for detecting a position or an attitude of an object from measured pixel positions in an image of a plurality of points on the object in consideration of a non-pinhole characteristic of a camera, the image being taken with one camera, the plurality of points on the object being in a known positional relationship, the position detecting method comprising the steps of: obtaining a position matrix indicating rotation and translation of the object from the measured pixel positions and a positional relationship between the plurality of points without considering the non-pinhole characteristic of the camera; obtaining a corrected pixel position corresponding to one of the measured pixel positions in consideration of the non-pinhole characteristic of the camera; adjusting the position matrix such that a distance between the corrected pixel position and the measured pixel position falls within an allowable range; and setting a position corresponding to the position matrix as the object position estimated in consideration of the non-pinhole characteristic of the camera, the position matrix being adjusted such that the distance between the corrected pixel position and the measured pixel position falls within an allowable range.