1. An imaging apparatus comprising: an image capturing unit which performs continuous image capturing; a storing unit which stores a plurality of first images captured by the image capturing unit before a shutter button is pushed, and a plurality of second images captured by the image capturing unit after the shutter button is pushed; a generating unit which generates a background image which is a single still image of a background of a dynamic body included in the first images and second images based on at least the plurality of first images; an extracting unit which extracts a dynamic body image which is an image of a dynamic body included in the second images by finding a difference between the background image and the second images; and a composing unit which generates a composition image by superimposing and composing on the background image the dynamic body image extracted from a first one of the second images captured after the shutter button is pushed, and superimposes and composes the dynamic body image extracted from a second or subsequent second images, on the composition image generated by composing the dynamic body image extracted from the second image immediately before to generate a plurality of composition images while maintaining the position relationship of each portion of the dynamic body with the background image.