PROBLEM TO BE SOLVED: To detect in which position on a road surface and in which degree range moisture is distributed by detecting the moisture of a relatively wide area. ;SOLUTION: A camera 10 for photographing a road surface 20 has sensitivity to the light of a wave length area absorbable in moisture. A sensor 12 measures light intensity on the road surface. An image digitalizer 14 converts a road surface image obtained from the camera into a digital image (a detecting object image). A memory device 28 stores a database stored by converting the road surface image obtained in various brightness environments in a dry state into the digital image. A reference image output device 30 reads out an image according to a measuring result of the sensor from the database, and outputs this image itself or an image by converting this image on the concentration as a reference image coincident with the measuring result of the sensor in brightness of an image pickup environment. A comparing processing device 32 receives the reference image according to brightness of the image pickup environment of a sent detecting object image from a reference image output device to be compared with the detecting object image.;COPYRIGHT: (C)2001,JPO
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