A radiation image-acquiring apparatus or a radiation image-acquiring method capable of reducing artifact due to pulsations of a heart of a subject to be examined is disclosed. X-rays generated by an X-ray generating portion and transmitted through the subject are detected as a two-dimensional distribution by a two-dimensional detector while the subject is rotated by a rotating table in an image-acquiring area formed by the X-ray generating portion and the two-dimensional detector, pulsation variations specific to the subject are detected, and a period p of the variation is calculated. A ratio q of a static time relative to the variation period p is then determined, a rotation time for one rotation is calculated based on the variation period p and the ratio q, and a rotating table is rotated.