This X-ray phase imaging apparatus (100) includes a controller (5) that generates a dark field image (Iv) with respect to each of a plurality of relative positions between a subject (S) and an imaging grating (G1) changed by an adjustment mechanism (3) to acquire a contrast of a region of interest (ROI) in the dark field image (Iv), and controls the adjustment mechanism (3) to adjust a relative position between the subject (S) and the imaging grating (G1) based on the acquired contrast.
