To provide an image processing type snow cover sensor on a road surface and a snow cover detecting method that are for detecting a snow cover on the road and precisely determine the presence of the snow cover without malfunction influenced by daily sunlight and shadows of buildings even when tire tracks of vehicles are left.

In the sensor and the method, the road surface is photographed by a camera; the image photographed by the camera is fetched into a computer as bitmap data to convert into an intensity image; the average intensity of a road indicating section is determined to compare with the intensity of a road surface other than the road indicating section; the snow cover is determined to exist when the ratio between the intensity of the road other than the road indicating section and the average intensity of the road indicating section is a fixed value or more; the intensity image is differentiated and an edge image is determined when the area of the snow cover is a reference value or less; and furthermore, the edge image is Haugh-transformed and it is determined that the snow cover exists when the number of line segments in parallel with a road direction are detected which is a predetermined number or larger.