A grid comprises an alternate assembly of radiation-permeable members and radiation-impermeable members which extend substantially parallel to the chest wall of a subject. When a radiation emitted from a radiation source is applied through a breast of the subject and the grid to a radiation detector, a radiation image of the breast is captured. While the radiation is being applied to the breast, the grid reciprocates in directions perpendicular to the direction in which the radiation-impermeable members extend.