Provided is a particle radiation therapy apparatus which can cause an X-ray imaging device to be retracted without unnecessarily occupying available space in a treatment room, thereby improving work efficiency for the medical staff. A particle radiation therapy apparatus 10 includes: a bed 15 that positions a patient 12； an irradiation port 16 (16a, 16b) that outputs, in a treatment room 11, a particle radiation beam transported through a fixed beam transport path； a horizontal direction imaging unit 21 that includes a first X-ray source 25 and a first X-ray detector 26 which are opposed along a horizontal line with the bed 15 therebetween； a vertical direction imaging unit 22 that includes a second X-ray source 27 and a second X-ray detector 28 which are opposed along a vertical line with the bed 15 therebetween； an accommodation chamber 18 which accommodates the first X-ray detector 26 under the floor when the horizontal direction imaging unit 21 is not in use； and a support member 23 that moves the first X-ray detector 26 so as to be above the floor and supports same between the bed 15 and the irradiation port 16 when the horizontal direction imaging unit 21 is in use.粒子線治療裝置(10)係具備有：床(15)，其係將患者(12)定位；照射口(16(16a、16b))，其係在治療室(11)輸出通過被固定的射束輸送路徑而被輸送的粒子線射束；水平方向攝影部(21)，其係包括以沿著水平線夾著床(15)的方式相對向的第1X線源(25)及第1X線檢測器(26)；垂直方向攝影部(22)，其係包括以沿著垂直線夾著床(15)的方式相對向的第2X線源(27)及第2X線檢測器(28)；收容室(18)，其係在水平方向攝影部(21)不使用時，使第1X線檢測器(26)收容在地板下；及支持構件(23)，其係在水平方向攝影部(21)使用時，使第1X線檢測器(26)移動至地板上而在床(15)與照射口(16)之側之間支持。
