Imaging device and method for taking an image and generating composite image data with appropriate exposure

An imaging device that shoots and records a moving image, the device comprising: an imaging section configured to repeatedly perform imaging at a cycle shorter than the frame rate of the moving image and output image data; an image processing section including a plurality of image composition processing, which is preliminarily determined, and configured to generate a composite image by performing image composition on a series of the image data, which are output from the imaging section, in one processing of the plurality of image composition processing; and an exposure calculation section configured to instruct, based on a field brightness, one processing of the plurality of image composition processing of the series of image data.