To lengthen the operating time by a secondary battery by converting electric power to kinetic energy or vice versa by means of an energy converter and opening or closing a part of an electric circuit to charge the secondary battery with the power generated by the energy converter.

A signal received by a receiving section 1 is transmitted to a processor 3 and the processor 3 supplies the power of a secondary battery 2 to an energy converter 5 through a diode 4 at a preliminarily set cycle. The energy converter 5 uses a motor with its rotary shaft being mounted with an accentric weight. The power supplied to the energy converter 5 is converted to kinetic energy and the reception of the signal is notified by vibration. A changeover switch 6 cuts out the connection between conductors (f) and (g) synchronously with the supply of power. In this notification method by vibration, the changeover switch 6 connects the conductors (f) and (g) each time the 'on' period is off and the supply of power from the secondary battery 2 stops, and thereby kinetic energy caused in a motor of the energy converter 5 is converted to electric energy, which reaches a charging circuit 8 and charges the secondary battery 2.