To restrain a rush current generated in driving a load of which impedance is changed depending on temperature.

This power supply device senses the temperature of an incandescent lamp 10 by a temperature sensor 6 when a switch S1 is turned on and controls the pulse width of a control pulse P output from a control circuit 7 based on the temperature sensed by the temperature sensor 6. Thereby, the device controls a time until a lamp terminal voltage applied to the incandescent lamp 10 reaches a predetermined voltage depending on the impedance of the incandescent lamp 10.