To provide a charge-discharge system which can certainly diagnose degradation of a storage battery.

Current on discharging operation of a lead storage battery 11 is measured by an ammeter 15, current volume is calculated from the current measured by the ammeter 15 at a controller 16 and this current volume is compared to that of a reference value. If the current volume measured during discharge is judged to be below that of the reference value, the lead storage battery is overcharged by raising output voltage of a reference voltage supply 14. The current volume on the discharging operation is measured again, and if an increasing volume of this current volume is predetermined volume or less, it is judged that the lead storage battery 11 is deteriorated.