1. An image registration device, comprising: a processor configured to: perform a rigid registration of a first input image with a second input image, which is a reference, to obtain first deformation information, perform a first non-rigid registration of the first input image with the second input image by taking the first deformation information as the initial deformation information to obtain second deformation information, perform a second non-rigid registration of the first input image with the second input image by taking the second deformation information as the initial deformation information to obtain third deformation information, and generate a registered image by performing a spatial transformation on the first or second input image by using the third deformation information.