A light source device includes a light source unit having a dielectric barrier discharge lamp and a lighting circuit. The lighting circuit includes a transformer; a switching element; a controller for the switching element; a detector that detects current flowing through or voltage on a primary or a secondary side of the transformer; and a determination unit. The controller is configured to enable performing a steady-state operation of controlling ON/OFF of the switching element at a steady-state operation frequency (f1) to steadily light the dielectric barrier discharge lamp; and a determination operation of controlling ON/OFF of the switching element at a determination operation frequency (f2) higher than the steady-state operation frequency (f1), and the determination unit determines whether or not to stop the lighting operation based on the current or the voltage detected by the detector when the controller controls the switching element at the determination operation frequency (f2).