To simply perform calibration irrespective of the dimension of a measuring space.

Calibration processing is executed by using images from two cameras 1a, 1b having equal focal lengths whose optical axes are arranged in parallel. The images from the cameras 1a and 1b are stored in picture image memories 4a and 4b, respectively. The image of the second camera 1b is displayed on a monitor 9. When an operator specifies, on the displayed image, a plurality of image points of an object point whose spatial coordinates are known, a coordinate processing part 6 extracts points corresponding to the specified points, on the input image from the camera 1a. By using the coordinated results and the positional relation of the cameras 1a, 1b, a calibration processing part 8 calculates stereo coordinates of each object point. By using the calculated results and the known spatial coordinates, parameters expressing the positional relation between a stereo coordinate system and a spatial coordinate system are calculated.