1. An imaging device including an image sensor, comprising: an image obtaining control unit that obtains plural continuous images of an object taken by the image sensor; a size determining unit that determines an image size of reduced images based on photographing information of at least one of the images, and generates the reduced images from the images obtained by the image obtaining control unit based on the determined image size; a motion vector detection unit that detects a motion vector of the reduced images; and an image synthesis unit that synthesizes the images obtained by the image obtaining control unit based on the motion vector detected by the motion vector detection unit to obtain a synthesized image.