A device includes a holder attached to the casing that is configured to hold an edge of a terminal device. A first clamper is arranged on a first wall of the holder, and a second clamper is arranged on a second wall opposing the first wall so that the first clamper faces the second clamper to exert a pinching force on the edge of the terminal device. A clamper interlocking component decreases the pinching force exerted by the first and second clampers when the edge of the terminal device is inserted toward a bottom surface of the holder, and increases the pinching force exerted by the first and second clampers when the edge of the terminal device is pulled away from the bottom surface of the holder.