A lighting circuit for lighting a semiconductor light source includes: a DC/DC converter configured to receive a DC first voltage and a DC second voltage and generate a DC third voltage; a first connector including a first terminal, wherein the third voltage is applied to the first terminal, wherein the first connector connects the first terminal and one end of the semiconductor light source; and a control circuit that controls the DC/DC converter. The control circuit selects only the first voltage as a voltage applied to the other end of the semiconductor light source, when a voltage for emitting the semiconductor light source is less than an absolute value of a difference between the first and second voltages. The control circuit selects the first voltage or the second voltage as the voltage applied to the other end thereof, when the voltage is not less than the absolute value.