A ultraviolet irradiation apparatus includes: an ultraviolet-irradiation water tank; a protection pipe provided in the ultraviolet-irradiation water tank; an ultraviolet lamp provided in the protection pipe to be 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; an electronic ballast provided in one of the protection covers; and a feeder wire electrically connecting the ultraviolet lamp to the electronic ballast. 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.