1. A radiation imaging apparatus comprising: a radiation emitting source that emits a radiation; a radiation detector that output, frame by frame, digital-quantity two-dimensional data corresponding to incidence of the radiation thereto; moving means for moving a pair of the radiation emitting source and the radiation detector, the radiation detector, or an object being imaged relatively to a remaining one among the radiation emitting source, the radiation detector, and the object; data acquiring means for acquiring, frame by frame, the data outputted from the radiation detector while the pair of the radiation emitting source and the radiation detector, the radiation detector, or the object is moved relatively to the remaining one by the moving means; and image producing means for producing a three-dimensional optimally focused image based on the data acquired by the data acquiring means, a portion to be imaged of the object in the three-dimensional optically focused image being optimally focused and reflecting an actual size and shape of the portion thereon.