A lighting device includes a first and a second gate circuit having a first input to which a high frequency square wave signal generated from a high frequency oscillation circuit is inputted and a second input to which a first low frequency square wave signal is inputted; and a second gate circuit having a first input to which the high frequency square wave signal is inputted and a second input to which a second low frequency square wave signal is inputted. Each of the first and the second low frequency square wave signal has a frequency lower than that of the high frequency square wave signal, and the first and the second low frequency square wave signal determine whether the high frequency square wave signal is supplied, as on/off switching signals, to the first and the second switching power supply circuit, respectively.