An illumination system includes a luminaire, a controller, and a switch that turns ON and OFF power supply to the luminaire. The controller includes: a light intensity controller that performs light intensity control of controlling the brightness of the luminaire; and a power supply controller that instructs the switch to turn OFF the power supply to the luminaire on which the light intensity control is performed at a light intensity rate that is equal to or greater than 0 and at most a predetermined value.