There is provided a particle therapy system including: a particle beam generator for generating a particle beam; an irradiation nozzle arranged in a treatment room and irradiating a target with the particle beam; a particle beam transport system 6 communicating the particle beam generator with the irradiation nozzle; an X-ray imaging device arranged in the treatment room and imaging the position of the target through irradiation with X-rays; a dosimeter 8 arranged at a position passed by the particle beam in the irradiation nozzle; and a control apparatus 400 performing control to exclude the measurement result of the X-rays from the measurement result obtained using the dosimeter 8 when the X-rays are emitted during treatment.