Particle beam treatment apparatus

A particle beam treatment apparatus comprising:

• an irradiator that has an irradiation nozzle which irradiates an irradiation target with a particle beam and that is capable of moving rotationally in a vicinity of the irradiation target;
• a moving floor that extends on an annular trajectory surrounding the irradiation target along a rotation circumferential direction of the irradiator and that is movable on the annular trajectory depending on a position of the irradiator;
• a movable cover that is supported pivotably with respect to the irradiator or the moving floor and that covers a gap between the irradiator and the moving floor;
• and
• an adjustor that includes a guide rail and that is configured to adjust a pivoting position of the movable cover depending on the position of the irradiator such that a gap between the movable cover and the moving floor is covered,
• wherein the movable cover includes
• a perpendicular cover portion that is positioned in a plane perpendicular to a rotation axis of the irradiator and that covers the gap between the irradiator and the moving floor when viewed from a direction of the rotation axis, and
• a parallel cover portion that is positioned in a plane parallel to the rotation axis of the irradiator.