To enable a liquid type storage battery and a seal type storage battery to be used in combination by performing the turning on and off of the contact interposed between one end of a first storage battery and one end of a second storage battery by the detection of the power failure of an AC power source and the detection of the voltage of the first or second storage battery.

For a DC power unit, a liquid type storage battery is used for the first storage battery 31, and a seal type storage battery is used for the second storage battery 32. The liquid type storage battery and the seal type storage battery can be installed in parallel by arranging the constitution such that the floating charge voltage VF for floatingcharging the liquid type storage battery and the equal charge voltage VE for equally charging it can be set in a first rectifying circuit 21, that the trickle charge voltage VT for trickle-charging the seal type storage battery can be set in a second rectifying circuit 22, and that the signal to turn off the contact 5 by detecting the voltage of the second storage battery 32 is sent out to a control circuit 6.