An illumination device includes a first light source and a second light source, a sensor, and a controller. The controller repeats a plurality of operation cycles, one operation cycle being a set of a first period in which only a detection target light source is caused to emit light and a second period in which the first light source and the second light source are caused to emit light. The sensor outputs detection values of detected light amounts in the first period. The controller controls the light source such that light amount of the light source fall in a target range, based on a detection result that corresponds to a value corresponding to the detection values of the light amount detected a predetermined number of times.