NOVELTY - The device (1) has a box-shaped main body (2) formed with an opening. An upper cover (4) opens and closes the opening. A rechargeable battery (8) is accommodated in the main body. An inverter device (5) is accommodated in the main body. The inverter device converts direct voltage from the battery to alternating square-wave voltage and outputs the voltage. A sine-wave adapter converts the square-wave alternating voltage output from the inverter device to sine-wave alternating voltage and outputs the sine-wave alternating voltage, where the adapter is accommodated in the main body.    USE - High-capacity emergency power supply device e.g. 12 volt (V) direct current (DC) power source and 100 V alternating current (AC) power source, for use in a power tool i.e. driver drill.    ADVANTAGE - The main body is provided with an inlet for external air at a side and a discharging fan at another side opposing the former side, so that temperature increase within the main body can be suppressed even if the battery and the sine-wave adapter generate heat. The device can be used for long period of time. The device can grasp temperature of the battery in an accurate manner. The battery or battery pack can be used by an operator, thus improving convenience of the device. The battery is supported by battery shafts at a position shifted forward slightly from a center along front-rear direction, so that distance between recessed portions accommodating wheels and an abutting section is large, thus downsizing the main body and reducing cost of the device. The wheels are provided at the main body, so that the device can be moved in an easy manner.    DETAILED DESCRIPTION - The battery is a lead storage battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a front cross-sectional view of a power supply device when an inverter device is accommodated in a main body.    High-capacity emergency power supply device (1)    Box-shaped main body (2)    Upper cover (4)    Inverter device (5)    Rechargeable battery (8)