An illumination device includes a light source, a position data acquirer configured to acquire position data indicating positions of a plurality of detection targets, a position data processor configured to calculate ellipse data corresponding to the positions of the detection targets based on the position data, a light quantity setter configured to set light quantity of the light source based on the ellipse data calculated by the position data processor, an irradiation shape setter configured to set an irradiation shape of light from the light source based on the ellipse data calculated by the position data processor, and an irradiation angle setter configured to set an irradiation angle of light from the light source based on the ellipse data calculated by the position data processor.