A dimming device includes a control unit, a first setting section and a second setting section. The control unit is configured to receive a control signal transmitted by a multiplexing transmission method and to control a dimming level of an illumination load in response to the control signal. The illumination load includes light-emitting diodes. The first setting section is configured to set a lower limit of the dimming level of the illumination load, the lower limit being adjustable in a first range. The second setting section is configured to set an upper limit of the dimming level of the illumination load, the upper limit being adjustable in a second range. A minimum value in the second range is greater than a maximum value in the first range.