To generate a distance image which indicates a distance between a camera and an object to be imaged by adjusting an image based on detected information of a zoom camera under a zoom condition and using an image converted with appropriate zoom scale and the other image.

The zoom condition of a standard camera 2 is detected by a detecting mechanism such as a potentiometer, a sensor signal corresponding to the zoom condition is sent to a sensor signal detecting part 10, and the zoom scale, an image center, and lens distortion to output voltage are determined with conversion tables or the like. A distance image generating part 12 initializes and optimizes the zoom scale, an optimal evaluation value, and a zoom scale optimum value, and conducts scale conversion of a reference image using the zoom scale, the image center, and lens distortion. The picture of the reference image is scaled down so as to become the identical size to the picture of the reference image used in calibration. The distance image generating part 12 conducts distance image generating process and evaluation value computing process based on the reference image after scale conversion.