1. A radiation imaging system for dividing a total image capture field into N integer number of small image capture fields, and producing a single continuous radiographic image from N number of division radiographic images obtained by division exposures of said small image capture fields, said radiation imaging system comprising: a radiation source for emitting radiation to each of said small image capture fields; a radiation image detecting device having a detection panel having an imaging surface having an arrangement of a plurality of pixels, said detection panel detecting said radiation that has passed through a body part of said small image capture field to produce said division radiographic image; a plurality of dose detection sensors substantially uniformly distributed in said imaging surface, each for measuring a radiation dose; a memory for storing an irradiation area map that defines as an irradiation area an area for measuring said radiation dose in accordance with said body part to be imaged; a map scaling section for scaling up or down said irradiation area map so as to make said irradiation area map coincide with said total image capture field in size; a dose detection sensor selector for selecting one or more of said dose detection sensors belonging to said irradiation area based on said irradiation area map that has been scaled up or down by said map scaling section; and an automatic exposure controller for automatically controlling a radiation exposure in each of said division exposures, said automatic exposure controller stopping emission of said radiation from said radiation source in accordance with a measurement value obtained from a detection signal of said dose detection sensor selected by said dose detection sensor selector.