When a shutter button of an electronic camera is depressed, the electronic camera photographs a subject and the photographed image data is stored into a main storage device of the electronic camera. Upon receiving a photography command from a computer connected to the electronic camera, a check is made to determine whether the main storage device of the electronic camera still holds image data to be processed. If the main storage device still holds image data to be processed, then an error signal is sent to a device from which the photography command is issued. If the main storage device does not hold image data to be processed, then the electronic camera photographs a subject and the photographed image is stored into the main storage device. Then, a notice of normal termination is sent to a device from which the photography command is issued. If the main storage device still holds image data to be processed, then the compressing, saving, or transferring of the image data in the main storage device is carried out on a predetermined data volume basis.