A power supply device using electromagnetic power generation includes an electric motor, an electromagnet, a winding, a rechargeable unit, and a battery case. The electromagnet is operatively connected to the electric motor so that an activation of the electric motor changes a magnetic field of the electromagnet. The winding is around the electromagnet so that the change of the magnetic field of the electromagnet generates emf in the winding. The rechargeable unit is electrically connected to both the electric motor and the electromagnet so that the emf is stored in the rechargeable unit or supply to an external electric load. The battery case includes an electrical wire electrically connected to the winding.