1. An imaging device, comprising: a main photography unit that photographs a photographic subject and acquires a photographic image; a preparatory image acquisition unit that performs preparatory photography before and/or after the main photography unit acquires the photographic image, and acquires preparatory images; a photographic information acquisition unit that acquires photographic information related to a circumstance of photography when the preparatory images are acquired by the preparatory image acquisition unit; a recording unit that records the photographic information and the photographic image upon a recording medium in mutual correlation; an intruding object detection unit that, when preparatory images have been acquired by the preparatory image acquisition unit before acquisition of the photographic image by the main photography unit, detects an intruding object into a photographic field on the basis of the photographic information that is acquired by the photographic information acquisition unit and specifies movement of the photographic subject; and a control unit that permits or prohibits photography by the main photographic unit, according to the result of intruding object detection by the intruding object detection unit.