An ultraviolet irradiation device includes: a pipe joint including a first connection part connectable to a first pipe extending in a first direction, a second connection part connectable to a second pipe extending in a second direction intersecting the first direction, and a main part positioned between the first connection part and the second connection part； and a light source configured to radiate ultraviolet light from the main part toward the interior of the first pipe. The ultraviolet irradiation device may include a window member provided in the main part and transmitting the ultraviolet light from the light source.
