A time-division control circuit individually controls an effective voltage supplied to each lighting load by adjusting the periods during which switching circuits connected to N sets of lighting loads are kept on. A zero-cross signal having a value that changes at the zero-cross point of the AC voltage is generated. An oscillation signal is generated with a frequency equal to, or an integer multiple of the AC frequency. The phase difference between the zero-cross signal and the oscillation signal is measured and a common reference point that defines the timing for turning the switching circuits ON or OFF is determined on the basis of the measured phase difference. An ON/OFF signal for each switching circuit is transmitted at a timing for each of the N sets of switching circuits on the basis of the reference point and the effective voltage to be supplied to the lighting load.