A particle beam irradiation chamber in which a passage having a first opening part at a side of an inner wall and a second opening part at a side of an outer wall is provided and which has an isocenter inside the chamber, wherein a first line segment which connects the center of the first opening part and the center of the second opening part passes inside the passage, an angle, which is formed by a second segment, which connects the center of the first opening part and the isocenter and the first line segment, is smaller than 180 degrees, and a width of the passage is narrower than a width of opening of the first opening part.
