PURPOSE: To provide a storage battery charging control system capable of preventing an overdischarge from being left to the utmost through a charging of a solar battery while providing a system capable of sufficiently using an extended load or fully utilizing an extended storage battery.

CONSTITUTION: A storage battery charging control system comprises current detecting means for detecting a strength and a direction of current flowing between a storage battery Bl and a storage battery B2 charged by generating means, voltage detecting means for detecting terminal voltages of both the storage batteries B1 and B2, and switch means for switching the intermediate path between both the storage batteries B1 and B2. When it is detected that the terminal voltage of the storage battery B1 exceeds a set voltage and is higher than that of the storage battery B2, the switch means is maintained to a close state and a control is performed so that the storage battery B2 is charged by the generating means. When it is detected that at least the terminal voltage of the storage battery B1 exceeds the set voltage or a current flows from the side of the storage battery B2 to the side of the storage battery B1, the switch means is maintained to an open state.