A calibrating apparatus for a zoom lens comprising: a first image-acquiring section 60 for acquiring a first image-for-calibration by photographing an area, in which reference marks for calibration are positioned, with a photographic device-to-be-calibrated 19 whose focal length is set to a first focal length; a second image-acquiring section 62 for acquiring a second image-for-calibration by photographing the area, in which the reference marks for calibration are positioned, with the photographic device-to-be-calibrated 19 whose focal length is set to a second focal length; a correction coefficient calculating section 64 for calculating a calibration correction coefficient for the first and second focal lengths, with the use of the photographed reference marks in the first and second image-for-calibrations: and a reference mark inferring section 66 for inferring a positional relationship of the photographed reference marks for calibration in the second image-for-calibration, with the use of the photographed reference marks for calibration in the first image-for-calibration.