To support a driver for safely driving a vehicle even when the visibility of the driver is lowered due to backlight of sunlight.

A driving support device 100 calculates position information of a vehicle at a predetermined time, calculates position information of the sun at the same time, and determines whether or not the sunlight becomes the backlight with respect to the vehicle at the time on the basis of whether or not the position of the sun is within a prescribed range with respect to the position of the vehicle. When determining that the sunlight becomes the backlight, the driving support device 100 reduces a ratio of the sunlight entering the field of view of the driver, or operates an in-vehicle device to output information for calling attention of the backlight to the driver.