An image on which a noise reduction and a dynamic range expansion process have been performed is generated by a sequential synthesis process using continuous-photographed images of different exposure conditions. The continuous-photographed images of different exposure conditions are input, configuration pixels of an input image and an intermediate synthetic image are classified into a noise pixel, an effective pixel, or a saturation pixel, a synthesis processing method of a pixel unit is decided according to a combination of pixel classification results of the corresponding pixels, and the intermediate synthetic image is updated according to the decided method. A 3DNR process is performed when at least one of the corresponding pixels of the input image and the intermediate synthetic image is the effective pixel, the pixel value of the intermediate synthetic image is output without change when both of the corresponding pixels of the input image and the intermediate synthetic image are the saturation pixel or the noise pixel, and the 3DNR process is performed or the pixel value of the intermediate synthetic image is output when one is the saturation pixel, and the other is the noise pixel.