A dielectric barrier discharge lamp (14) has an inside electrode (142) in a tube axis direction within the airtight container (141), which has ultraviolet transmission properties and a long tube shape, and an outside electrode (143) having a semicircular shape arranged outside of the airtight container (141) in close contact with it. Besides, an excimer-forming gas is sealed in the airtight container (141). AC voltage supplied from the power source (11) is converted into DC voltage through a converter (12) and outputted. A high-frequency wave is generated by an inverter (13) based on the DC voltage supplied from the converter (12), and a dielectric barrier discharge is induced in the dielectric barrier discharge lamp (14) to irradiate ultraviolet rays. The converter (12) is configured by connecting in series the outputs of DC power sources (121), (122). Optimum luminous efficiency of a dielectric barrier discharge lamp having different specifications is also realized by adjusting the number of DC power sources.