Ultraviolet irradiation apparatus

An ultraviolet irradiation apparatus comprising:

• an ultraviolet irradiation water tank having a water-inlet port for water to be treated and a water-outlet port for treated water;
• a protection pipe provided in the ultraviolet irradiation water tank, and penetrating two ends of the ultraviolet-irradiation water tank;
• an ultraviolet lamp provided in the protection pipe, and configured to emit ultraviolet rays onto the water to be treated by being lit up with high-frequency discharge at a frequency of 10 kHz to 10 MHz, inclusive;
• protection covers respectively provided on the two ends of the ultraviolet-irradiation water tank and configured to block the ultraviolet rays and electromagnetic waves;
• an electronic ballast provided in one of the protection covers;
• and
• a feeder wire provided in the ultraviolet-irradiation water tank and the protection covers and electrically connecting the ultraviolet lamp to the electronic ballast, wherein
• each of the ultraviolet-irradiation water tank and the protection covers is made of a conductive material with a specific conductivity and a relative magnetic permittivity whose product is equal to or larger than 1, and has a thickness at least three times as large as a skin depth at a frequency of a high-frequency current that flows through the ultraviolet lamp.