PURPOSE: To prolong the cycle life by suppressing the dispersion of the capacity at charge and discharge in an unsettled discharge of a battery thereby putting it in chargeable condition.

CONSTITUTION: When a charge control circuit 5 detects a secondary battery 3 being connected, the supply of a function formation end signal S1 to a function generator 6 is stopped, and an indicator lamp 5a is lit. The function generator 6 generates a charge current geared to the objective current value i* having spectrum distribution approximately conforming to the the spectrum distribution of the discharge current at the the time of unsettled discharge of a secondary battery 3, and this charge currents charges the secondary battery 3. As a result, the dispersion of each cell to the charge of the secondary battery 3 decreases, and the cycle life of the secondary battery 3 can be prolonged.