A hadron therapy installation comprising: an irradiation unit with a horizontal axis of rotation capable of rotating around a treatment area; a moving floor (8', 8") in the form of a band deformable in the longitudinal direction and guided in a guide structure, comprising a segment on either side of said irradiation unit; and a traction mechanism arranged between said irradiation unit and said two segments of said moving floor (8', 8"), such that said irradiation unit can drive said floor segments via that traction mechanism when it rotates about its axis of rotation; characterized in that said traction mechanism comprises: a rigid traction frame surrounding said irradiation unit with functional play on either side thereof and supported by said irradiation unit such that said rotating irradiation unit can move relative to said traction frame within the limits of said functional play, said segments (8', 8") of said floor being connected said rigid traction frame on either side thereof; and force transmitting means arranged between said traction frame and said irradiation unit so as to freeze said traction frame in a central position relative to said irradiation unit, as long as the force transmitted by said force transmitting means remains below a threshold value, said force transmitting means comprising at least one safety element that gives way when the transmitted force exceeds said threshold value, to allow a relative movement of said irradiation unit with respect to said traction frame taking hereby advantage of said functional play. an irradiation unit with a horizontal axis of rotation capable of rotating around a treatment area; a moving floor (8', 8") in the form of a band deformable in the longitudinal direction and guided in a guide structure, comprising a segment on either side of said irradiation unit; and a traction mechanism arranged between said irradiation unit and said two segments of said moving floor (8', 8"), such that said irradiation unit can drive said floor segments via that traction mechanism when it rotates about its axis of rotation; characterized in that said traction mechanism comprises: a rigid traction frame surrounding said irradiation unit with functional play on either side thereof and supported by said irradiation unit such that said rotating irradiation unit can move relative to said traction frame within the limits of said functional play, said segments (8', 8") of said floor being connected said rigid traction frame on either side thereof; and force transmitting means arranged between said traction frame and said irradiation unit so as to freeze said traction frame in a central position relative to said irradiation unit, as long as the force transmitted by said force transmitting means remains below a threshold value, said force transmitting means comprising at least one safety element that gives way when the transmitted force exceeds said threshold value, to allow a relative movement of said irradiation unit with respect to said traction frame taking hereby advantage of said functional play. a rigid traction frame surrounding said irradiation unit with functional play on either side thereof and supported by said irradiation unit such that said rotating irradiation unit can move relative to said traction frame within the limits of said functional play, said segments (8', 8") of said floor being connected said rigid traction frame on either side thereof; and force transmitting means arranged between said traction frame and said irradiation unit so as to freeze said traction frame in a central position relative to said irradiation unit, as long as the force transmitted by said force transmitting means remains below a threshold value, said force transmitting means comprising at least one safety element that gives way when the transmitted force exceeds said threshold value, to allow a relative movement of said irradiation unit with respect to said traction frame taking hereby advantage of said functional play.