DC or DC power source unit with a battery charging function

A DC power source unit supplies a DC voltage or DC voltage to an operated with electric power tool through an adapter to a battery and also loads column, which is used as an alternative power source of the tool. In the DC-power source unit of the invention, a microcomputer receiving a temperature signal indicating a temperature of the power column, and determines that the battery pack is fully charged based on the temperature signal. This determination is performed regardless of whether the battery pack is being charged or not. As such, the fully charged state of the battery pack itself can then be accurately detected when the tool is operated when the battery pack is almost fully charged.