1. A position detecting method with which to detect a position of a picked-up image, the position detecting method comprising: preparing a plurality of templates with which correlation values of a picture-element data distribution, as a pick-up result of the image, are calculated and which correspond to same reference images of which center positions are spaced a predetermined distance apart; obtaining, by calculating correlation values between the picture-element data distribution and the plurality of templates, position of a maximum template whose correlation value is maximal; obtaining at least one of a curved line function and curved surface function which fit a distribution of correlation values of the correlation values calculated, the center of the distribution being present in the maximum template's position; and calculating position of the picked-up image based on the at least one function.