Object sensing device and method for windscreen wiper

An object sensing device and an object sensing method in which a threshold does not have to be adjusted or updated even under the influence of external light are provided. The object sensing device includes a light source (20;30;90) for irradiating a sensing surface (110), which is an external surface of a transparent substrate (100), an imaging optical system lens (40) for forming an image by a light from the sensing surface, and a photo-detector array (50) for receiving the image formed by the imaging optical system lens, the photo-detector array including a plurality of photo-detectors (51). The photo-detector array receives the light from the imaging optical system lens, and outputs a signal pattern that is an arrangement of light detection signals from the respective photo-detectors according to an arrangement of the photo-detectors and corresponds to a condition of an object present on the sensing surface. The object sensing device further includes a difference part for obtaining a differential signal of signal outputs from adjacent photo-detectors among the plurality of the photo-detectors according to the arrangement in the photo-detector array, and an object judging part for judging a presence of the object by detecting a presence of a pair of a positive peak and a negative peak in a pattern of the differential signal obtained by the difference part.