PURPOSE: To provide an image contour extracting device for extracting the contour of an image under a condition irradiated. with natural light even in the case an inputted image includes the linear elements of all the spatial frequencies, furthermore, a body moving at extremely high speed is the object to be processed.

CONSTITUTION: The device is constituted of a polarization modulating means 210 for receiving read-out light and write-in light so as to change the polarization angle of the read-out light in accordance with the light intensity of the write-in light, a means 200 for supplying the light of the inputted image to the polarization modulating means 210 as the write-in light, an image reading means 220 for supplying the light polarized in one direction to the polarization modulating means 210 as the read-out light, a polarized image outputting means 230 for transmitting the light polarized at a prescribed angle out of the light outputted from the polarization modulating means 210 and outputting the light. A relative angle between a polarization direction of the polarization modulating means 210 in terms of properties and the polarization angle of the read-out light is set at a prescribed angle. Furthermore, the image inputting means 200 is provided with a means for adjusting the light intensity of the inputted image, the focal depth of the image and the focus of the image.