The objective of the present invention is to provide a particle radiotherapy device which does not require too much space between a scanning electromagnet and a subject being irradiated, and for which a ridge filter that can be easily produced can be used. This particle radiotherapy device comprises an irradiation unit (18) which further comprises a scanning electromagnet (5) for scanning a particle beam that proceeds inside a vacuum duct (4) and irradiating a subject with the particle beam and a beam extraction window (7a, 7b) for extracting the particle beam from the vacuum duct into the air, wherein the irradiation unit is constituted such that the vacuum duct is separably provided at a flange surface (47) more toward the side of the subject being irradiated than the scanning electromagnet, and when a scanning type irradiation vacuum duct (6) provided more toward the side of the subject being irradiated than the flange surface is moved so as not to overlap a beam line (1) of the particle beam, a ridge filter (42) for broad beam irradiation can be mounted in the space which is on the beam line of the particle beam and in which the scanning type irradiation vacuum duct was provided before being moved.La présente invention a pour but de proposer un dispositif de radiothérapie par particules qui ne nécessite pas trop despace entre un électroaimant de balayage et un sujet qui est irradié, et pour lequel un filtre de nervure qui peut être facilement produit peut être utilisé. Ce dispositif de radiothérapie par particules comprend une unité dirradiation (18) qui comprend en outre un électroaimant de balayage (5) pour balayer un faisceau de particules qui avance à lintérieur dun conduit sous vide (4) et irradier un sujet avec le faisceau de particules et une fenêtre dextraction de faisceau (7a, 7b) pour extraire le faisceau de particules à partir du conduit sous vide dans lair, lunité dirradiation étant constituée de sorte que le conduit sous vide soit disposé de manière
