1. An imaging apparatus comprising: a first imaging control means for periodically imaging; a first detection means for detecting a predetermined photographic subject from an image data imaged by the first imaging control means; an instruction means for instructing to imaging still-image during periodic imaging by the first imaging control means; a second imaging control means for imaging still-image when instructed by the instruction means; a second detection means for detecting a predetermined photographic subject from a still-image data imaged by the second imaging control means; a comparison means for comparing a result of the photographic subject detection by the first detection means with a result of the photographic subject detection by the second detection means; and an informing means for informing a comparison result by the comparison means.