An ultraviolet sterilization device (10, 110, 210) comprising: a processing chamber housing (150, 250) that defines a processing chamber (112, 212) that is a cylindrical member extending from a first end (151, 251) toward a second end (152, 252) in an axial direction and in which a fluid that is a subject of sterilization flows; a light source (141, 240) provided to radiate ultraviolet light in the axial direction toward an opening of the first end of the processing chamber housing such that ultraviolet light enters an interior of the processing chamber; a window member (124, 224) provided in the vicinity of the first end so as to provide a gap relative to the first end and transmitting the ultraviolet light from the light source, and an outer flow passage (116, 216) which is provided outside the processing chamber (112, 212) and in which the fluid passing through the processing chamber flows, characterized in that a wall of the processing chamber is a stack structure (130, 230) including a first layer (131, 231) made of polytetrafluoroethylene (PTFE) having a thickness of 3 mm or larger and a second layer (132, 232) made of aluminum (Al), the first layer being provided on an inner side of the processing chamber and at least a part of the wall of the processing chamber is a partition wall positioned between the processing chamber and the outer flow passage, the partition wall being a stack structure (130, 230) including the first layer (131, 231), the second layer (132, 232), and a third layer (133, 233) of a fluororesin material stacked in the stated order, and the first layer being positioned toward the processing chamber and the third layer being positioned toward the outer flow passage. a processing chamber housing (150, 250) that defines a processing chamber (112, 212) that is a cylindrical member extending from a first end (151, 251) toward a second end (152, 252) in an axial direction and in which a fluid that is a subject of sterilization flows; a light source (141, 240) provided to radiate ultraviolet light in the axial direction toward an opening of the first end of the processing chamber housing such that ultraviolet light enters an interior of the processing chamber; a window member (124, 224) provided in the vicinity of the first end so as to provide a gap relative to the first end and transmitting the ultraviolet light from the light source, and an outer flow passage (116, 216) which is provided outside the processing chamber (112, 212) and in which the fluid passing through the processing chamber flows, characterized in that a wall of the processing chamber is a stack structure (130, 230) including a first layer (131, 231) made of polytetrafluoroethylene (PTFE) having a thickness of 3 mm or larger and a second layer (132, 232) made of aluminum (Al), the first layer being provided on an inner side of the processing chamber and at least a part of the wall of the processing chamber is a partition wall positioned between the processing chamber and the outer flow passage, the partition wall being a stack structure (130, 230) including the first layer (131, 231), the second layer (132, 232), and a third layer (133, 233) of a fluororesin material stacked in the stated order, and the first layer being positioned toward the processing chamber and the third layer being positioned toward the outer flow passage.