An electric power control method according to an aspect of the present disclosure includes determining a control threshold value at a start of a demand time period based on a demand target value, measuring an amount of demand electric power of a customer which has received an electric power supply from an external power source and consumed electric power from the start of the demand time period to an arbitrary time point during the demand time period, updating the control threshold value based on the measured amount of demand electric power and the demand target value, and supplying electric power to the customer from a distributed power source when an instantaneous value of an electric power consumption of the customer exceeds the control threshold value during the demand time period.