1. An imaging apparatus comprising: an image capturer configured to generate a plurality of short-exposure images by performing continuous imaging for a first time in a first imaging mode in which imaging is performed through exposure over the first time; a processor configured to control the image capturer to generate at least one short-exposure image through performing additional imaging after the first time if an imaging command is input in a state where the first imaging mode and an HDR (High Dynamic Range) mode are set; and an image processor configured to synthesize the short-exposure images generated by the image capturer by successively accumulating the short-exposure images, wherein the processor is further configured to control the image processor to generate an HDR image by synthesizing a first image in which a first number of short-exposure images from among the plurality of short-exposure images that are generated for the first time are successively accumulated, generate a second image in which the plurality of short-exposure images that are generated for the first time are successively accumulated, and generate a third image in which the second image and the at least one short-exposure image that is generated after the first time are accumulated.