PROBLEM TO BE SOLVED: To provide a crop growth level measuring system based on the crop image extracted from a farming field image taken from the sky so as to diminish the assaying error for the crop taken slantly. SOLUTION: This measuring system works as follows: a near-infrared image obtained by taking a farming field 1 from the sky with a photographic section 43 and the quantity of near infrared incident sunlight measured by an incident light measuring section 41 enter an arithmetic processing section 47 based on the taken image and the quantity of incident light, an image with the reflectance of the near- infrared component as data is generated at a reflectance image generating section 474b and then binarized at a binarized image generating section 474c to generate a binarized image where crop portion and the other portion are separated from each other subsequently, the crop image is extracted from the binarized image at a binarized image corrective section 474d and corrected to an image to be obtained by taking from right above using the crop image thus corrected, the IR output from the crop is calculated at an IR output calculating section 474e and the aimed crop growth level is calculated based on the IR output at a growth level calculating section 474f.
