A deposit detection device according to an embodiment includes a detection module and a storage processing module. The detection module detects a deposit region corresponding to a deposit adhering to an imaging device, based on brightness information of an image captured by the imaging device. The storage processing module stores deposit information on the deposit region in a storage unit that is nonvolatile, when an ignition power of a vehicle is turned off in a state in which the deposit region is detected. For an initial detection process after the ignition power is turned on, the detection module detects the deposit region based on the deposit information stored in the storage unit.