1. An image processor comprising: an image input unit configured to input a multiple image in which images of a subject are superimposed on each other; an inter-superimposed-image deformation acquisition unit configured to acquire deformation information between superimposed images included in the multiple image input through the image input unit; an image deformation unit configured to generate at least two deformed images by performing deformation processing with respect to the multiple image input through the image input unit at least twice to be geometrically deformed based on the deformation information between superimposed images acquired by the inter-superimposed-image deformation acquisition unit; a signal intensity relationship acquisition unit configured to acquire signal intensity relationship information indicative of a relationship between signal intensities of the superimposed images included in the multiple image input through the image input unit; and a signal processing unit configured to perform addition processing of the at least two deformed images generated by the deformation processing by using the signal intensity relationship information acquired by the signal intensity relationship acquisition unit.