To decrease the charging frequency of a battery power source and to increase a wait time by using a photovoltaic generation means as a main power source and a battery power source as an auxiliary power source and charging the battery power source with excessive electric power of the photovoltaic generation means by an electric power control means.

When the electric power generated by the photovoltaic generation means 21 is large enough to drive respective system constituent elements, the power control means 19 drives the system constituent elements with the electric power generated by the photovoltaic generation means 21 through a main CPU 15. When the power control means 19 judges that the electric power generated by the photovoltaic generation means 21 is much larger than the power needed to the system constituent elements, the battery power source 17 is charged with its excessive power. When light is not enough and the sufficient electric power is not supplied to the respective system constituent elements, the power control means 19 drives the respective system constituent elements through the CPU 15 with the electric power of the battery power source 17 and the electric power of the photovoltaic generation means 21. Consequently, the use frequency of the battery power source 17 is decreased to compensate a decrease of the electric power of the battery power source 17.