A data transfer control system includes a PC and a camera, and these are
connected by a USB cable in a manner capable of making a communication
with each other. Prior to a data transfer, the PC instructs the camera
that it is impossible to cut-off, that is, to prohibit a connected state
(connection state) from being released. In receipt thereof, the camera
turns-on a cut-off-impossible lamp. Upon completion of the data transfer
and a transfer of FAT data, the PC instructs the camera that it is
allowed to cut-off, that is, to allow to release the connection state. In
receipt thereof, the camera turns-off the cut-off-impossible lamp.