1. A cell culture device provided with a storage container capable of forming a space sealed off from outer atmosphere, in which the following devices are disposed: an incubator for cell culturing; a light source for irradiating light to the cells in culture process in the incubator; and an image acquiring device for imaging the cells in culture process, placed in the back of the incubator with respect to the light source, as well as comprising means for processing images acquired by the image acquiring device and means for creating image data for extracting the cells, wherein the image data creating means comprises: means for selecting at least two images having clear periphery of the cells from the images acquired by changing the focal point positions; means for adjusting positions of the selected images; and means for carrying out the differential processing on the aligned images, and wherein the image acquiring device is disposed as movable in light source direction, and acquires the cell images of each focal point positions.