Abstract: The radiation imaging device acquires incident position information of radiation for each detector by setting the size of a through-hole such that at least one pixel is arrayed in a plane view from a direction perpendicular to the detector plane; arranges a septa in displacing from a boundary line between a detector pair in a plane view from a direction perpendicular to the detector plane; further arranging the septa so as to be orthogonal to the boundary line between the detector pair in a plane view from a direction perpendicular to the detector plane; arranges the top of the through-hole in a plane view from a direction perpendicular to the detector plane, in displacing from the boundary line of the detector pair; and arranges the top of the detectors in a plane view from a direction perpendicular to the detector plane so as to be visible through the through-hole.