1. An imaging device, comprising: an imaging circuit to obtain image data by imaging an object; an image synthesis circuit to synthesize synthesis image data using the image data; an image synthesis estimation circuit to estimate whether an object possibly to be synthesized is included or not in the image synthesis circuit; and an image capturing instruction circuit to instruct the imaging circuit to capture an image, wherein the image capturing instruction circuit instructs the imaging circuit to capture a plurality of images according to an estimation result of the image synthesis estimation circuit, wherein the image synthesis estimation circuit instructs the imaging circuit to capture the plurality of images in a plurality of different conditions, obtains a plurality of estimation image data sets to be used for the estimation, analyzes the plurality of estimation image data sets, and thereby performs determination whether image synthesis is to be performed or not according to the plurality of conditions, and wherein the image synthesis estimation circuit changes at least one of the plurality of conditions, causes the plurality of estimation image data sets to be obtained, analyses a movement amount of the object, and performs the determination whether the image synthesis is to be performed or not, depending on the movement amount.