An electric power control system of the present invention includes an electric power supplying means, a load means, and an energy storing means. The electric power control system includes: an energy storage controlling means for controlling the energy storing means so as to decrease charge or discharge electric power over a response time corresponding to a set time constant for energy storing means; and a supplied energy controlling means for executing control to change electric power supplied by the electric power supplying means over a response time corresponding to a set time constant for electric power supplying means so that the electric power supply and demand difference is kept within the preset given range. The time constant for energy storing means is set to be longer than the time constant for electric power supplying means.