PURPOSE: To enable to suitably charge a battery in response to the state of the battery by detecting the capacity of the battery on the basis of the charging current of the battery, and stopping the charging operation of a main circuit when the capacity of the battery becomes full.

CONSTITUTION: When a start switch 4 is closed, a controller 3 starts a main circuit 2, which starts charging a battery 7. A charging meter 8 integrates the charging current of the battery to integrate the product of the battery capacity or terminal voltage represented by the total electric amount and the charging current of the battery to obtain the battery capacity represented by the total power amount, and outputs a charge stop signal 202 to the controller 3 when the battery capacity coincides with the full charging capacity. The charging operation of the main circuit is also stopped by closing a manual stop switch 5.