A method and device for safety protection of a secondary battery capable of preventing smoking and ignition thereof. A lithium cell 1 as a chargeable and dischargeable secondary battery, a protection circuit 11 for shutting down charging power Pc at the time of overcurrent, overvoltage, etc., and an electric power restriction circuit 20 for limiting the charging power Pc input to the lithium cell 1 are incorporated into a battery pack 10. A battery charger 12, equipped with a stabilized electric source 13 and a charging circuit 14, inputting the charging power Pc to the lithium cell 1, is connected to a previous stage of the battery pack 10. The electric power restriction circuit 20 limits the charging power Pc within a boundary value Pmax of a safety operation region for safely using the lithium cell 1, thereby permitting the lithium cell 1 to operate safely under any conditions.