A safe electric power regulating circuit is connected between a power supply and a voltage boost/buck circuit to regulate the output voltage by the power supply to have a target voltage through the voltage boost/buck circuit. A switching device includes a switch unit, a first diode, and a first capacitor. The switch unit includes a first end, a second end, and a third end. The first end is connected to the power supply, and the second end is connected to the voltage boost/buck circuit. The switch unit is controlled to connect the third end to the first end or the second end. The first diode has one end connected to the first end of the switch unit. The first capacitor has one end connected to the third end of the switch unit and the other end connected to circuit ground.