One of first through fourth target state of charge levels, which are set at values that increase gradually over time, is selected on the basis of an ON/OFF state of a specific current consumer installed in the vehicle and a state of charge immediately preceding an engine stoppage. A target state of charge is set on the basis of the selected target state of charge level and an elapsed time after the lead storage battery is installed in the vehicle, whereupon the target state of charge is compared with the actual state of charge of the lead storage battery. The lead storage battery is charged in accordance with the comparative result.