An adhering substance detection apparatus includes calculating, first and second detecting, and generating units. The calculating unit calculates a variation in a feature value related to luminance in past and current captured images captured by an image capturing device, based on the luminance of pixels included in the captured images. The first detecting unit detects a first region in which the variation calculated by the calculating unit falls within a threshold range, and the feature value in the current captured image falls within a threshold range. The second detecting unit detects a second region in which an irregularity in a distribution of the luminance of the pixels included in the captured image satisfies a predetermined irregularity condition. The generating unit generates a sum region being a sum of the first and second regions, as an adhering substance region corresponding to an adhering substance adhering to the image capturing device.