To provide a charger for secondary battery pack, capable of performing optimal charging control by applying optimal charging voltage to a secondary battery body in the charger.

A voltage-monitoring part 16 of the charger 18 directly monitors the terminal voltage of the secondary battery body 13 through a voltage- monitoring terminal 19, so that the charger 18 controls the charging of the secondary battery body 13. A voltage drop occurs in an electronic switch 11 at charging, however, the monitoring voltage for charging control is obtained directly from the secondary battery body 13, so that voltage control is performed by the terminal voltage of the secondary battery body 13 without being affected by the voltage drop in the electronic switch 11. The charger 18 controls the charging so as to take the terminal voltage of the secondary battery body 13 as a threshold for stopping charging in full-charge, thus it is possible to always apply the optimal charging voltage to the secondary battery body 13, even if the voltage drop in the electronic switch 11 fluctuates.