There is provided a rain sensor capable of adequately detecting raindrops in a captured image. The rain sensor includes: a surface light source 14 which emits light to a windshield G to cause light to be incident on a raindrop detection region T set on the windshield G at a critical angle or more; a camera 15 which is arranged on the optical path of light totally reflected by the detection region T and captures the detection region T; and a detection unit which detects raindrops adhering to the detection region T from contrast in the image captured by the camera 15; the detection unit detects the raindrops adhering to the detection region T based on at least one of the captured image in the detection region T to which light is emitted from the surface light source 14 and the captured image in the detection region T to which light is not emitted from the surface light source 14.