To provide a technique to obtain a synthesized image with an expanded dynamic range with ease and a technique to reduce workload of a user while maintaining the degree of freedom relating to image processing. There provides an image inputting part taking in at least one of a plurality of low-resolution images and a high-resolution image obtained by shooting the same subject while changing exposure condition, a shift detecting part detecting a positional shift of pictorial pattern between each of the plurality of low-resolution images and the high-resolution image, and a gradation expanding part generating a synthesized image in which a range of reproduced gradation is expanded by performing position alignment between each of the plurality of low-resolution images and the high-resolution image based on the positional shift, extracting a gradation information of the plurality of low-resolution images, and synthesizing it with the high-resolution image.