A reflection determining apparatus is configured to determine reflection for a camera, wherein the camera is configured to photograph an external environment of a vehicle through a glass from an inside of the vehicle and the camera includes a reflection preventer configured to prevent reflection on the glass. The reflection determining apparatus is provided with: a calculator configured to calculate an optical flow of an area in which the reflection is not prevented in a photographed image of the camera; and a determinator configured to determine that there is the reflection in the photographed image of the camera if a duration in which a particular area is detected is greater than or equal to a predetermined time, wherein the particular area is defined by points with a value of the optical flow that is smaller than a predetermined threshold value.