Provided is a power supply device, which is capable of coping with semiconductor light source loads to be set in various ways, and has high efficiency, in which a current to be supplied to each of the loads has a small ripple. The power supply device supplies power to a semiconductor light source load and lights the semiconductor light source load, and includes: a DC-DC converter; and a controller. The DC-DC converter includes an inductance element and a switching element, and performs voltage conversion by storing energy in the inductance element from an input power source when the switching element is on, and discharging the energy, the energy being stored in the inductance element, to a load side when the switching element is off. The controller controls ON/OFF operations of the switching element so that an output current of the DC-DC converter can be the same as a target value. In the power supply device, means for regulating timing of turning on the switching element so that a current flowing through the inductance element can flow in a continuous mode operation is provided at least in the controller.