A deposit detection device according to an embodiment includes a calculation module, a detection module, an interpolation module, and a state management module. The calculation module calculates a region feature amount based on an edge vector of each pixel, for each unit region composed of a predetermined number of pixels included in a captured image. The detection module detects the unit region corresponding to a partial covering location and the unit region corresponding to a diffuse reflection location based on a detection condition and a second detection condition, respectively, the first detection condition and the second detection condition being based on the region feature amount. The interpolation module interpolates the area ratio of the partial covering location reduced due to the diffuse reflection location. The state management module controls state transitions of states related to interpolation of the area ratio, based on increase and decrease of the diffuse reflection location.