Abstract: The invention relates to an electronic book system (a contents display method) that functionally or efficiently displays information related to reading or advertisement in a small display area on a display of a portable reading terminal, the portable reading terminal receives digitized book contents and digitized related information proper to the contents via the Internet and the related information is displayed together with the book contents on the portable reading terminal by operating a button of the portable reading terminal or operator guidance on the display screen.

Abstract: A DC power source light which is mountable to and dismountable from a camera body of a video camera is supplied with power from a battery provided in said camera body so that said DC power source light is made compact and light in weight. Further, either said camera body or said DC power source light has a unit for preventing excess discharge of said battery and a unit for preventing excess current when the switch is turned on, thereby to protect said battery.