The inventive control circuit 40 serves to render the output voltage to be the output value of any one of the outputs OUT1 to OUT5 when both the main power source A of the power saving device 100 and the control circuit's switch B are in ON state, and to maintain the output value to be constant by the operations of the comparator, CPU or the like in the control circuit 40. In addition, if the input voltage or input current is excessively high or low, the control circuit 40 can cut off the voltage or current, so that the protection device 100 can be protected from abnormal voltage or abnormal current.