A light detection device includes a light projector, a light receiver, a detector, and a controller. The light projector projects light to a predetermined range. The light receiver has a light receiving region in which light is received. The detector detects light by comparing a light reception result by the light receiver with a predetermined threshold. The controller controls the threshold. The controller shifts in turn a range where light is projected from the light projector. The controller, causes the detector to detect light per a portion of the light receiving region, the portion corresponding to a range with light being projected from the light projector, and sets the threshold based on a light reception result by the light receiver in a different portion of the light receiving region from the portion corresponding to the range with light being projected.