A load leveling system and a method for a power system are capable of attaining load leveling in a distribution substation unit. The load leveling system is for a power system with a controller having a major customer and lower transforming apparatus, and with a customer connected to the lower transforming apparatus via a low-voltage line. The system also has a communication unit between the customer and its own system, and control use time zones of devices within the customer, as well as an electric demand prediction unit, and a first load leveling processing unit. By employing such a system, it becomes possible to provide a load leveling system for a power system that is capable of realizing load leveling of both a distribution substation unit and a pole transformer unit.