A white turbid state diagnostic apparatus has an imaging part installed on a vehicle and configured to convert a light signal from a periphery of the vehicle into an image signal, a region detection part configured to detect a region from the image signal, the region being constituted by pixels having brightness values over a predetermined brightness and being in a substantially circular shape having a predetermined area or more, a brightness gradient calculation part configured to calculate a brightness gradient on a line which is directed from a predetermined position in a predetermined direction based on brightness values of pixels on the line in the region, and a white turbid level calculation part configured to calculate a white turbid level of the lens based on the brightness gradient.