A frequency control method includes segmenting a range from a predetermined reference frequency to a predetermined lower limit frequency or a predetermined upper limit frequency into frequency range segments according to a number of battery apparatuses, detecting a current frequency of a power system, and causing battery apparatuses to charge from the power system or discharge to the power system in order to control a frequency or maintain a supply and demand balance of the power system, causing lager number of battery apparatuses to charge or discharge as a frequency range segment including the current frequency becomes farther apart from the reference frequency.