Radiation imaging system and radiation imaging method

In a radiation imaging system and radiation imaging method according to the present invention, a system control unit comprises: a still image generation unit for generating, on the basis of a still imaging request, a still image by synthesizing radiation images of a plurality of continuous frames acquired by means of radiation imaging performed at a set frame rate; a movement amount prediction unit for, before the still imaging request, predicting the amount of movement of a subject among the plurality of frames after the still imaging request, on the basis of the radiation images acquired by means of the radiation imaging performed at the set frame rate; and a synthesis frame number determination unit for determining a frame number for obtaining the still image, in accordance with the predicted amount of movement of the subject.