To provide a safer charging system for a lithium ion battery pack, which achieves a proper full-charged state according to the battery state.

The charging system 200 includes: a battery pack 20; and a charging device 1 which charges a secondary battery cell 21 with its voltage and current set to a predetermined value and has a charging control circuit for stopping charging when the charging voltage of the battery pack reaches a full-charged state or an overcharged state. The charging system further has a battery state detection means 28 for detecting the state value of the secondary battery cell 21 relating to the variation in the charging state of the secondary battery cell 21. A charging voltage setting means 30(microcomputer 14) determines a charging voltage setting value (Y-K) in response to the state value (Cc) (e.g. battery temperature) of the secondary battery cell 21 detected by the battery state detection means 28.