A plurality of illumination devices is respectively disposed on a ceiling surface at a plurality of grid points formed on the ceiling surface which is partitioned into a grid. A detector unit detects the attendance status for a plurality of seats that respectively exists corresponding to the positions of the plurality of grid points. A control device can communicate with each of the plurality of illumination devices. The control device has a dimming information generation unit that generates, for each group set in accordance with each attended position, one group being defined as a block formed by a plurality of grid points centered on the attended position, dimming information for the illumination device to be dimmed within a group. The control device also has a transmission unit for transmitting the dimming information. The illumination device to be dimmed in the plurality of illumination devices performs dimming on the basis of the received dimming information.